Method for joining dissimilar metal materials and joint

Abstract

To provide a bonding method for dissimilar metal materials capable of improving a bond strength, and a bonding joint for dissimilar metal materials bonded by the above bonding method.SOLUTION: A bonding method for dissimilar metal materials comprises: a process of preparing a steel plate 1 (a first plate material) to arrange an aluminum alloy plate 2 (a second plate material) having a first through hole 2a on the face orthogonal to the thickness direction of the steel plate 1; a process of inserting an element 4 having a second through hole 4a into the hole 2a; and a process of fusing a part each of the steel plate 1 and element 4 by an arc spot welding to form a weld metal 5 having the same main component as that of the steel plate 1. Before the process of forming the weld metal 5, a gap part 7 of 0.1 mm or more but 2.0 mm or less is formed between the area surrounding at least the first through hole 2a and a face facing the aluminum alloy plate 2 of the steel plate 1 in the face facing the steel plate 1 of the alloy plate 2.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for joining dissimilar metal materials that can join plate materials made of different materials with high strength, and to a welded joint of dissimilar metal materials joined by the above joining method. [Background technology]

[0002] Automobiles and other transportation equipment are constantly being challenged to improve fuel economy in order to reduce various factors, including (a) the consumption of finite petroleum fuels, (b) the greenhouse gas CO2 emitted during combustion, and (c) vehicle costs. This can be achieved through improvements in powertrain technologies, such as the use of electric drivetrains, as well as by reducing vehicle weight. One way to achieve this is to replace the current primary steel material with lightweight materials such as aluminum or aluminum alloys, magnesium or magnesium alloys, and carbon fiber. However, replacing everything with these lightweight materials poses challenges, such as high cost and insufficient strength. As a solution, a so-called multi-material design approach, which combines steel and lightweight materials in the right places, has been gaining attention. Hereinafter, aluminum or aluminum alloys and magnesium or magnesium alloys will sometimes be referred to simply as aluminum alloys and magnesium alloys.

[0003] Patent Document 1 discloses an arc spot welding method for joining dissimilar metals, which joins a first plate made of an aluminum alloy or magnesium alloy to a second plate made of steel, as a method for joining a first plate made of a second aluminum alloy or magnesium alloy to a second steel plate. The arc spot welding method described in Patent Document 1 includes the steps of drilling a hole in the first plate, overlapping the first plate and the second plate, inserting a steel auxiliary joining member having a stepped outer shape with an insertion portion and a non-insertion portion and having a hollow portion passing through the insertion portion and the non-insertion portion into the hole in the first plate, and filling the hollow portion of the auxiliary joining member with weld metal and welding the second plate to the auxiliary joining member by a predetermined method. It also describes that this welding method can produce a strong and highly reliable joining. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-034164 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the above-described joining method, in which an auxiliary joining member is inserted into a hole in a first plate, the hollow portion of the auxiliary joining member is filled with weld metal, and the second plate and the auxiliary joining member are welded together, may not provide the desired joint strength. In particular, when joining in a narrow space is required, the hole in the first plate must be made small. Therefore, the hollow portion of the auxiliary joining member inserted into this hole becomes even smaller, and the area of ​​the joint becomes extremely narrow, resulting in a lower joint strength compared to when a sufficiently large hole is made in the first plate.

[0006] The present invention has been made in consideration of such problems, and aims to provide a method for joining dissimilar metal materials that can improve joining strength, and a welded joint of dissimilar metal materials joined by the above-mentioned joining method. [Means for solving the problem]

[0007] The above object of the present invention is achieved by the following configuration [1] relating to a method for joining dissimilar metal materials.

[0008] [1] A step of placing a first plate material and a second plate material made of a material different from the first plate material and having a first through hole on a surface perpendicular to a thickness direction of the first plate material; a step of melting a portion of the first plate material through the first through hole by arc spot welding and forming a weld metal having the same main component as the first plate material, A method for joining dissimilar metal materials, comprising the step of forming a gap of 0.1 mm or more and 2.0 mm or less between an area surrounding the first through hole on the surface of the second plate material facing the first plate material and the surface of the first plate material facing the second plate material, before the step of forming the weld metal.

[0009] Further, preferred embodiments of the present invention relating to a method for joining dissimilar metal materials relate to the following [2] to

[10] .

[0010] [2] The method for joining dissimilar metal materials described in [1], characterized in that in the step of forming the weld metal, the first through hole is filled and a weld having a diameter larger than the diameter of the first through hole is formed on the upper surface of the second plate material, thereby joining the first plate material and the second plate material.

[0011] [3] Before the step of forming the weld metal, Inserting an element having a second through hole into the first through hole; The element has an insertion portion formed on one axial end side of the second through hole and having a diameter capable of being 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 the diameter of the first through hole, The method for joining dissimilar metal materials according to [1], characterized in that in the step of forming the weld metal, a part of the first plate material and at least a part of the element are melted, and a weld metal that fills the second through hole is formed.

[0012] [4] The method for joining dissimilar metal materials described in [3], characterized in that in the step of forming the weld metal, the surface of the second plate material facing the first plate material and the surface of the element facing the first plate material are on approximately the same plane.

[0013] [5] The step of forming the void portion includes: a step of arranging a spacer between the first plate member and the second plate member at a position excluding a region that forms the gap; and placing the second plate on a surface of the first plate perpendicular to the thickness direction of the first plate, The method for joining dissimilar metal materials according to any one of [1] to [4], characterized in that the gap is formed in the area where the spacer is not placed by the step of placing the second plate material.

[0014] [6] The step of forming the void portion includes: forming a recess in at least one of the first plate material and the second plate material at a position including a region where the gap is to be formed, the recess having a shape spaced apart from the other plate material; and placing the second plate on a surface of the first plate perpendicular to the thickness direction of the first plate, The method for joining dissimilar metal materials according to any one of [1] to [4], characterized in that the void portion is formed in the region where the recess is formed by the step of placing the second plate material.

[0015] [7] The step of forming the void portion includes: forming a protrusion in a shape that protrudes toward the other plate material in a position on at least one of the first plate material and the second plate material excluding an area where the void portion is formed; and placing the second plate on a surface of the first plate perpendicular to the thickness direction of the first plate, The method for joining dissimilar metal materials according to any one of [1] to [4], characterized in that the step of placing the second plate material forms the void portion in an area where the convex portion is not formed.

[0016] [8] A method for joining dissimilar metal materials according to any one of [1] to [7], characterized in that the first plate material is either an aluminum or aluminum alloy plate, or a steel plate, and the second plate material is the other.

[0017] [9] In the step of forming the weld metal, the first plate material is melted to a surface opposite to the surface facing the second plate material to form a back wave, After the step of forming the weld metal, the size of the back wave is measured, and the joining strength between the second plate material and the first plate material is measured, and a relationship between the size of the back wave and the joining strength is obtained; The method for joining dissimilar metal materials according to any one of [1] to [8], characterized in that the joining strength is predicted based on the distance of the gap between the second plate material and the first plate material.

[0018]

[10] Prepare a first plate material for preliminary testing and a second plate material for preliminary testing having a through hole; Before the step of forming the weld metal, a step of forming a preliminary test gap between the first plate material for preliminary test and the second plate material for preliminary test, and conducting a preliminary welding test in the same manner as the step of forming the weld metal; The preliminary welding test involves a process of melting the surface of the first preliminary test plate material opposite to the surface facing the second preliminary test plate material to form a back wave, and a process of measuring the size of the back wave and measuring the joint strength between the first preliminary test plate material and the second preliminary test plate material, the process being carried out multiple times with the preliminary test gaps set at different intervals to determine the relationship between the spacing of the preliminary test gaps and the joint strength, The method for joining dissimilar metal materials according to any one of [1] to [8], characterized in that, based on the above relationship, a spacing of the preliminary test void portion that will result in the required joining strength is selected, and then a step of forming a void portion of the selected spacing is carried out.

[0019] The above object of the present invention is achieved by the following configurations

[11] and

[12] relating to a welded joint of dissimilar metal materials.

[0020]

[11] a first plank; a second plate member having a first through hole; a weld metal including a portion of the first plate, filling the first through hole, and having a weld metal with a diameter larger than the first through hole on a surface of the second plate opposite to a surface facing the first plate, A joint for dissimilar metal materials, characterized in that the first plate material and the second plate material are separated to form a gap at least around the periphery of the weld metal between the first plate material and the second plate material, and the spacing of the gap is 0.1 mm or more and 2.0 mm or less.

[0021]

[12] a first plank; a second plate member having a first through hole; an element having a second through hole inserted into the first through hole; a weld metal including a portion of the first plate material and a portion of the element and formed inside the second through hole, The element has an insertion portion formed on one axial end side of the second through hole and having a diameter capable of being 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 the diameter of the first through hole, A joint for dissimilar metal materials, characterized in that the first plate material and the second plate material are separated to form a gap at least around the periphery of the weld metal between the first plate material and the second plate material, and the spacing of the gap is 0.1 mm or more and 2.0 mm or less.

[0022] Further, preferred embodiments of the present invention relating to a welded joint of dissimilar metal materials relate to the following

[13] to [7].

[0023]

[13] A joint of dissimilar metal materials as described in

[11] or

[12] , characterized in that a spacer is disposed between the first plate material and the second plate material in an area excluding at least the gap and the weld metal.

[0024]

[14] A joint of dissimilar metal materials as described in

[11] or

[12] , characterized in that a recess having a shape that separates it from the other plate material is formed in at least one of the first plate material and the second plate material in a region that includes at least the gap and the weld metal.

[0025]

[15] A joint of dissimilar metal materials as described in

[11] or

[12] , characterized in that at least one of the first plate material and the second plate material in an area excluding at least the gap and the weld metal has a convex portion formed thereon that protrudes toward the other plate material.

[0026]

[16] The protrusion is formed on the second plate member so as to surround the first through hole, a recessed portion having a shape spaced apart from the first plate material and surrounding the protruding portion is formed in a region on the opposite side of the first through hole with respect to the protruding portion, the recess has a hole side wall portion on the first through hole side and an outer wall portion facing the hole side wall portion,

[15] A joint of dissimilar metal materials, characterized in that the hole side wall portion is higher than the outer wall portion.

[0027]

[17] A joint of dissimilar metal materials as described in

[16] , characterized in that a sealant that fills the gap between the first plate material and the second plate material is provided in the area opposite the first through hole with respect to the convex portion. [Effects of the Invention]

[0028] According to the present invention, it is possible to provide a method for joining dissimilar metal materials that can improve the joining strength, and a welded joint of dissimilar metal materials joined by the above-mentioned joining method. [Brief explanation of the drawings]

[0029] [Figure 1A] FIG. 1A is a cross-sectional view showing a method for joining dissimilar metal materials according to a first embodiment of the present invention in the order of steps. [Figure 1B] FIG. 1B is a cross-sectional view showing the step subsequent to that shown in FIG. 1A, illustrating the method for joining dissimilar metal materials according to the first embodiment of the present invention. [Figure 1C] FIG. 1C is a cross-sectional view showing the step subsequent to that of FIG. 1B, illustrating the method for joining dissimilar metal materials according to the first embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing a joint joined by the method for joining dissimilar metal materials according to the first embodiment of the present invention. [Figure 3] FIG. 3 is a cross-sectional view showing the state of the arc when the gap G1 between the steel plate and the aluminum alloy plate is set to 0 mm in the first embodiment. [Figure 4] FIG. 4 is a cross-sectional view showing a part of a method for joining dissimilar metal materials according to a second embodiment of the present invention. [Figure 5] FIG. 5 is a cross-sectional view showing the state of the arc when the gap G1 between the steel plate and the aluminum alloy plate is set to 0 mm in the second embodiment. [Figure 6] FIG. 6 is a cross-sectional view showing a part of a method for joining dissimilar metal materials according to a third embodiment of the present invention. [Figure 7] FIG. 7 is a cross-sectional view showing a part of a method for joining dissimilar metal materials according to a fourth embodiment of the present invention. [Figure 8] FIG. 8 is a cross-sectional view showing a part of a method for joining dissimilar metal materials according to a fifth embodiment of the present invention. [Figure 9] FIG. 9 is a graph showing the relationship between the nugget diameter and the uranami diameter, with the ordinate representing the nugget diameter and the abscissa representing the uranami diameter. [Figure 10]FIG. 10 is a graph showing the relationship between tensile shear strength and nugget diameter, with the vertical axis representing tensile shear strength and the horizontal axis representing nugget diameter. [Figure 11] FIG. 11 is a perspective view showing a combination of dissimilar metal materials in which a steel plate having a hat-shaped cross section is placed on a flat aluminum alloy plate as a first plate material. [Figure 12] FIG. 12 is a graph showing the relationship between the diameter of the back waves and the interval G1, with the vertical axis representing the diameter of the back waves and the horizontal axis representing the interval G1. [Figure 13] FIG. 13 is a graph showing the relationship between the nugget diameter and the gap G1, with the vertical axis representing the nugget diameter and the horizontal axis representing the gap G1. [Figure 14] FIG. 14 is a photograph showing a cutaway view of the comparative example and the example. DETAILED DESCRIPTION OF THE INVENTION

[0030] The inventors of the present application have conducted various studies on arc welding methods that can improve the joint strength of dissimilar metals compared to conventional methods. First, they investigated the reason why the desired strength cannot be obtained when joining dissimilar metals by a method in which the lower plate and upper plate are joined through a hole in the upper plate by melting the lower plate and forming a weld metal that fills the hole. As a result, it was found that the inner diameter of the hole in the upper sheet has a significant effect on the joint strength between the lower sheet and the upper sheet. That is, when the inner diameter of the hole is large, the arc spreads sufficiently, and the nugget diameter at the joint interface between the lower sheet and the upper sheet becomes large, thereby obtaining sufficient joint strength. On the other hand, when the inner diameter of the hole is small, the arc spread is hindered by the inner wall of the hole, resulting in a small nugget diameter and reduced joint strength.

[0031] Next, the present inventors investigated methods for increasing the nugget diameter to improve joint strength. When a sufficient area can be secured for the joint, simply increasing the inner diameter of the hole in the upper sheet is sufficient. However, as described above, when joining is required in a narrow area, the inner diameter of the hole cannot be increased. Therefore, the present inventors discovered that if a gap is provided at an appropriate interval between the lower and upper sheets around the periphery of the hole in the upper sheet, sufficient arc spread can be ensured even when the inner diameter of the hole is small, resulting in a larger nugget diameter and improved joint strength.

[0032] The inventors of the present invention have also found that there is a correlation between the size of the back ribs formed after welding and the nugget diameter, and between the nugget diameter and the joint strength. In other words, by measuring the size of the back ribs, it is possible to predict the joint strength, and therefore to select the optimal gap spacing. The present invention was made based on these findings.

[0033] Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiment described below, and can be implemented with any modifications within the scope of the gist of the present invention.

[0034] [Method for joining dissimilar metal materials] First Embodiment 1A to 1C are cross-sectional views showing the order of steps in a method for joining dissimilar metal materials according to a first embodiment of the present invention. Also, Fig. 2 is a cross-sectional view showing a joint joined by the method for joining dissimilar metal materials according to the first embodiment of the present invention. This embodiment is a method for joining a steel plate (first plate material) 1 and an aluminum alloy plate (second plate material) 2 by element arc spot welding.

[0035] As shown in FIG. 1A , a cylindrical first through hole 2a is formed in the aluminum alloy plate 2 at a position where the steel plate 1 is to be joined. In this embodiment, a void 7 is formed around the periphery of the first through hole 2a between the steel plate 1 and the aluminum alloy plate 2. Therefore, a spacer 3 is placed in a position between the steel plate 1 and the aluminum alloy plate 2, excluding the area where the void is to be formed. The spacer 3 may be formed by stacking multiple thin plate-like members to achieve a desired thickness, or a resin agent or the like may be applied to predetermined positions on the steel plate 1 or the aluminum alloy plate 2. When a plate-like member is used, the shape may be an annular plate-like member having a hole in the area where the void is to be formed, or multiple plate-like members of any shape that can be placed in a portion excluding the area where the void is to be formed. When a resin agent or the like is applied, the position is not particularly limited, and it may be applied so that the void 7 is formed in the desired area.

[0036] 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 allows insertion into the first through hole 2a of the aluminum alloy plate 2 is formed on one axial end side of the second through hole 4a. Furthermore, a head portion 4c having a diameter larger than the diameter of the first through hole 2a is formed on the other axial end side of the second through hole 4a of the element 4.

[0037] 1B , the aluminum alloy plate 2 is positioned so that the second through hole 4a overlaps the intended joining position on the steel plate 1, and the aluminum alloy plate 2 is placed on a surface perpendicular to the thickness direction of the steel plate 1. The element 4 may be inserted into the first through hole 2a after the aluminum alloy plate 2 has been placed on the upper surface of the steel plate 1. In this way, a gap 7 is formed between the lower surface of the aluminum alloy plate 2, i.e., the surface facing the steel plate 1, and the upper surface of the steel plate 1, i.e., the surface facing the aluminum alloy plate 2. Specifically, the gap 7 is formed between the upper surface of the steel plate 1 and a surface of the lower surface of the aluminum alloy plate 2 that surrounds at least the first through hole. The gap 7 is formed so that the distance G1 between the steel plate 1 and the aluminum alloy plate 2 is 0.1 mm or more and 2.0 mm or less.

[0038] Thereafter, as shown in FIG. 1C, a steel welding wire 9 held by a welding torch (not shown) is placed above element 4, and a current is passed through welding wire 9 while a shielding gas is flowed from gas nozzle 8 provided at the tip of the welding torch, thereby generating an arc 11.

[0039] 2, the welding wire 9 is melted through the second through hole 4a of the element 4 inserted into the first through hole 2a, and a part of the steel sheet 1 and at least a part of the element 4 are melted. As a result, the second through hole 4a is filled and a weld metal 5 having the same main components as the steel sheet 1 is formed.

[0040] In this embodiment, the element 4, the steel plate 1, and the weld metal 5 all have the same main components, and are therefore firmly fixed together by welding. Furthermore, the aluminum alloy plate 2 is physically fixed to the steel plate 1 by the head 4c of the element 4. Therefore, a welded joint 20 can be obtained in which the steel plate 1 and the aluminum alloy plate 2 are joined with high strength.

[0041] For comparison, the spread of the arc when the gap G1 between the steel plate 1 and the aluminum alloy plate 2 is 0 mm, i.e., when the steel plate 1 and the aluminum alloy plate 2 are arranged in contact with each other, will be described with reference to the drawings. Fig. 3 is a cross-sectional view showing the state of the arc when the gap G1 between the steel plate 1 and the aluminum alloy plate 2 is 0 mm in the first embodiment. In Fig. 3, the same components as those in Fig. 1C are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0042] As shown in FIG. 3, when the steel plate 1 and the aluminum alloy plate 2 are in contact with each other, the inner wall of the second through hole 4a prevents the arc 11 from spreading.

[0043] On the other hand, according to the joining method of the first embodiment as described above, the spacer 3 is arranged so that the gap G1 between the steel plate 1 and the aluminum alloy plate 2 in the gap 7 is 0.1 mm or more and 2.0 mm or less. Therefore, the arc 11 is sufficiently widened, and a sufficiently large reverse bead 12 is formed. In addition, the nugget diameter N1 at the joining interface between the steel plate 1 and the aluminum alloy plate 2 can be made larger than the nugget diameter N2 shown in Fig. 3 above, and the joining strength can be improved.

[0044] In this specification, the nugget diameter refers to the diameter of the weld metal at the interface where plate materials are joined, i.e., between a steel plate 1 and an aluminum alloy plate 2. As shown in Fig. 2 above, when the steel plate 1 and the aluminum alloy plate 2 are separated from each other, the nugget diameter refers to the diameter of the weld metal on the surface of the steel plate (first plate material) 1 facing the aluminum alloy plate (second plate material) 2.

[0045] If the gap G1 between the steel plate 1 and the aluminum alloy plate 2 in the gap 7 is less than 0.1 mm, the arc 11 cannot be sufficiently spread, making it difficult to sufficiently improve the joining strength. Therefore, the gap G1 in the gap 7 is set to 0.1 mm or more, preferably 0.2 mm or more, and more preferably 0.3 mm or more. On the other hand, if the upper limit of the gap G1 of the gap 7 exceeds 2.0 mm, depending on the welding conditions, the arc may penetrate the steel plate 1, resulting in poor welding or a smaller diameter of the back rib, which may reduce the joint strength. Furthermore, if the upper limit of the gap G1 of the gap 7 exceeds 2.0 mm, this may affect the structure of the resulting joint and complicate the manufacturing process. Therefore, the gap G1 of the gap 7 is set to 2.0 mm or less.

[0046] Furthermore, the width of the gap 7 in the direction perpendicular to the thickness direction of the steel plate 1 and the aluminum alloy plate 2 is not particularly limited, but is set to be larger than the diameter of the first through hole 2a. Since the arc becomes larger as the interval G1 of the gap 7 increases, it is preferable to set the width of the gap 7 according to the interval G1 of the gap 7.

[0047] In the first embodiment, the axial length of the insertion portion 4b of the element 4 is approximately the same as the plate thickness of the region where the first through hole 2a is formed in the aluminum alloy plate 2. If the axial length of the insertion portion 4b is shorter than the plate thickness of the aluminum alloy plate 2, a gap is formed between the lower surface of the element 4 and the upper surface of the steel plate 1, and the arc 11 can be spread. However, since the inner wall surface of the first through hole 2a in the aluminum alloy plate 2 is exposed, depending on the welding conditions, a part of the aluminum alloy plate 2 may be melted by the arc 11, and a brittle intermetallic compound may be formed at the interface between the steel plate 1 and the aluminum alloy plate 2.

[0048] Furthermore, if the axial length of the insertion portion 4b is longer than the plate thickness of the aluminum alloy plate 2, even if a gap portion 7 is formed between the steel plate 1 and the aluminum alloy plate 2, the element 4 may hinder the spread of the arc, and the effect of the gap portion 7 may not be fully obtained.

[0049] Therefore, it is preferable that the axial length of the insertion portion 4b of the element 4 is approximately the same as the plate thickness of the region where the first through hole 2a is formed in the aluminum alloy plate 2. In other words, it is preferable to design the size of the element 4 so that the lower surface of the aluminum alloy plate 2 (the surface facing the steel plate 1) and the lower surface of the element 4 (the surface facing the steel plate) are approximately flush with each other.

[0050] <Second embodiment> Fig. 4 is a cross-sectional view showing a part of a method for joining dissimilar metal materials according to a second embodiment of the present invention. The second embodiment shown in Fig. 4 differs from the first embodiment shown in Figs. 1A to 1C only in that the element 4 is not used. Therefore, in Fig. 4, the same components as those in Fig. 1C are given the same reference numerals, and detailed description thereof will be omitted.

[0051] In the second embodiment, an aluminum alloy plate 2 having a first through hole 2a is placed on a steel plate 1 via a spacer 3. No element is used at this time. Then, by arc spot welding, a welding wire 9 is melted through the first through hole 2a, and a portion of the steel plate 1 is melted to form a weld metal 15 that fills the first through hole 2a. Furthermore, a reinforcement 15a having a diameter larger than the first through hole 2a is formed on the upper surface of the steel plate 1. In this way, the steel plate 1 and the aluminum alloy plate 2 are joined together.

[0052] In this embodiment, no element is used, but since the steel plate 1 and the weld metal 15 have the same main component, they are firmly fixed together by welding. In addition, a reinforcement 15a is formed on the upper surface of the aluminum alloy plate 2, and this reinforcement 15a corresponds to the head 4c of the element 4 in the first embodiment. Therefore, since the aluminum alloy plate 2 is physically fixed to the steel plate 1 by the reinforcement 15a of the weld metal 15, the steel plate 1 and the aluminum alloy plate 2 can be joined with high strength.

[0053] Here, similarly to the first embodiment, the case where the gap G1 between the steel plate 1 and the aluminum alloy plate 2 is 0 mm will be compared with the second embodiment. Fig. 5 is a cross-sectional view showing the state of the arc when the gap G1 between the steel plate 1 and the aluminum alloy plate 2 is 0 mm in the second embodiment. In Fig. 5, the same components as those in Fig. 4 are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0054] As shown in FIG. 5, when the steel plate 1 and the aluminum alloy plate 2 are in contact with each other, the inner wall of the first through hole 2a prevents the arc 11 from spreading.

[0055] On the other hand, in the joining method according to the second embodiment, the spacer 3 is arranged so that the gap G1 between the steel plate 1 and the aluminum alloy plate 2 in the gap 7 is 0.1 mm or more and 2.0 mm or less. Therefore, the arc 11 spreads sufficiently, and the nugget diameter N3 at the joining interface between the steel plate 1 and the aluminum alloy plate 2 can be made larger than the nugget diameter N4 shown in Fig. 5 above, thereby improving the joining strength.

[0056] <Third embodiment> Fig. 6 is a cross-sectional view showing a part of a method for joining dissimilar metal materials according to a third embodiment of the present invention. The third embodiment shown in Fig. 6 differs from the first embodiment shown in Figs. 1A to 1C only in that a convex portion is provided on the second plate material instead of the spacer 3. Therefore, in Fig. 6, the same components as those in Fig. 1B are given the same reference numerals, and detailed description thereof will be omitted.

[0057] 6, in the third embodiment, an aluminum alloy plate 22 is provided with a first through hole 22a and a protrusion 22b that protrudes toward the steel plate 1. The position of the protrusion 22b is a position excluding the region that forms the void 7, and can be, for example, an annular shape formed at a position spaced a predetermined distance from the first through hole 22a.

[0058] In the third embodiment as well, the welding wire is melted, and at the same time, a part of the steel plate 1 and the inner wall surface of the second through hole 4a of the element 4 are melted to form a weld metal that joins them, thereby joining the steel plate 1 and the aluminum alloy plate 22. Furthermore, since the convex portions 22b of the aluminum alloy plate 2 are designed so that gaps 7 are formed in areas between the steel plate 1 and the aluminum alloy plate 22 where no convex portions 22b are formed, and the spacing G1 of the gaps 7 is 0.1 mm or more and 2.0 mm or less, the arc spreads sufficiently and high joining strength can be obtained.

[0059] In this embodiment, the aluminum alloy plate 22 serving as the upper plate is provided with the protrusion 22b. However, in the present invention, the steel plate 1 (first plate) may be provided with a protrusion that protrudes toward the aluminum alloy plate 22 (second plate). Even with this configuration, a gap with a gap G1 of 0.1 mm or more and 2.0 mm or less can be formed. In this embodiment, a gap 17 with a gap G2 is formed on the opposite side of the protrusion 22b from the first through hole 22a, and a sealant or the like can be placed in this gap 17. The effect of placing a sealant will be described later.

[0060] <Fourth embodiment> Fig. 7 is a cross-sectional view showing a part of a method for joining dissimilar metal materials according to a fourth embodiment of the present invention. The fourth embodiment shown in Fig. 7 differs from the third embodiment shown in Fig. 6 only in the shape of the aluminum alloy plates. Therefore, in Fig. 7, the same components as those in Fig. 6 are given the same reference numerals, and detailed description thereof will be omitted.

[0061] 7, in the fourth embodiment, an aluminum alloy plate 32 is provided with a first through hole 32a and a recess 32b that is spaced apart from the steel plate 1. The recess 32b is located at a position that includes a region that forms the gap 7, and can be, for example, a circular region that includes the first through hole 32a.

[0062] In the fourth embodiment, similarly to the third embodiment, the steel plate 1 and the aluminum alloy plate 32 can be joined together. Moreover, the recessed portion 32b of the aluminum alloy plate 2 is designed so that the gap 7 is formed in the region where the recessed portion 32b is formed between the steel plate 1 and the aluminum alloy plate 22, and the gap 7 has a distance G1 of 0.1 mm or more and 2.0 mm or less, and therefore the arc spreads sufficiently and high joining strength can be obtained.

[0063] In this embodiment, the recess 32b is provided in the aluminum alloy plate 22, which is the upper plate, but in the present invention, a recess having a shape spaced apart from the aluminum alloy plate 22 (second plate) may be provided in the steel plate 1 (first plate). Even with this configuration, a gap having a gap G1 of 0.1 mm or more and 2.0 mm or less can be formed.

[0064] <Fifth embodiment> Fig. 8 is a cross-sectional view showing a part of a method for joining dissimilar metal materials according to a fifth embodiment of the present invention. The fifth embodiment shown in Fig. 8 differs from the third embodiment shown in Fig. 6 in the shape of the aluminum alloy plates and the placement of a sealant. Therefore, in Fig. 8, the same components as those in Fig. 6 are given the same reference numerals, and detailed descriptions thereof will be omitted.

[0065] 8, in the fifth embodiment, an aluminum alloy plate 22 is provided with a first through hole 22a and a protrusion 22b that protrudes toward the steel plate 1. Therefore, a gap 7 is formed between the steel plate 1 and the aluminum alloy plate 2 inside the position where the protrusion 22b is formed, i.e., on the first through hole 22a side. Furthermore, a recess 21 that surrounds the protrusion 22b is formed on the opposite side of the first through hole 22a from the protrusion 22b. The recess 21 is composed of a hole side wall 21a on the first through hole side and an outer wall 21b that faces the hole side wall 21a, and is designed so that the hole side wall 21a is higher than the outer wall 21b.

[0066] When the aluminum alloy plate 22 configured in this manner is placed on the steel plate 1, a gap 7 with a distance G1 of 0.1 mm or more and 2.0 mm or less is formed in the region where the weld metal is formed. Furthermore, in the region opposite the first through hole 22a with respect to the recess 21, a gap 17 with a distance G2 is formed between the steel plate 1 and the aluminum alloy plate 22. Furthermore, in the region where the recess 21 is formed, a gap 27 with a distance G3 is formed between the steel plate 1 and the aluminum alloy plate 22.

[0067] In the fifth embodiment, as in the first to fourth embodiments, the gap 7 having the gap G1 of 0.1 mm or more and 2.0 mm or less is formed, so that the steel plate 1 and the aluminum alloy plate 22 can be joined with high strength. Furthermore, in this embodiment, a sealant 44 can be arranged in the region excluding the gap 7, i.e., the gap 17 and the gap 27, so as to surround the gap 7.

[0068] In this embodiment, the aluminum alloy plate 22, which is the upper plate, is provided with the convex portion 22b and the concave portion 21, but in the present invention, the steel plate 1 may be provided with a convex portion that protrudes toward the aluminum alloy plate 22 and a concave portion in an area opposite the first through hole 22a from the convex portion. Even with this configuration, it is possible to similarly form a gap portion with a gap G1 of 0.1 mm or more and 2.0 mm or less, a gap with a gap G2, and a gap with a gap G3.

[0069] Here, the effect obtained by this embodiment when the sealant 44 is disposed will be described. For example, as shown in the first to fifth embodiments, when a steel plate and an aluminum alloy plate are arc-welded via a first through-hole provided in the aluminum alloy plate, if moisture penetrates into the contact area between the dissimilar metals, corrosion is likely to occur. To prevent this, one method for preventing moisture from penetrating the contact area is to dispose a sealant around the contact area.

[0070] However, simply placing a sealant around the intended joining position, which will be the contact area between dissimilar metals, can cause the sealant to penetrate into the intended joining position. When arc welding is then performed, the sealant will volatilize, forming blowholes in the weld metal and resulting in poor welding.

[0071] In this embodiment, even when the sealant 44 is disposed so as to surround the gap 7, which is the intended joining position, the protrusions 22b formed on the aluminum alloy plate 22 can prevent the sealant 44 from entering the gap 7, thereby preventing the occurrence of welding defects. Furthermore, if the sealant 44 is disposed in the region of the gap 17, even when the sealant 44 is pushed and spread in a direction approaching the gap 7 when the aluminum alloy plate 22 is placed on the steel plate 1, the gap 27 is larger than the gap 17 in the gap 17, so the sealant 44 remains in the gap 27. This further enhances the effect of preventing the sealant 44 from entering the gap 7, preventing the occurrence of welding defects, thereby maintaining high joining strength between the steel plate 1 and the aluminum alloy plate 22.

[0072] When a sealant having low or no fluidity is used, the sealant can be used as the spacer 3 in the first and second embodiments as shown in Figures 1A to 1C and 4. As described above, in the third embodiment shown in Figure 6, the aluminum alloy plate 22 has the protrusions 22b formed thereon, so that the sealant can be placed in the gap 17 surrounding the protrusions 22b, and the same effect as in the fifth embodiment can be obtained.

[0073] In a third embodiment shown in FIG. 6, the height of the protrusion 22b corresponds to the spacing G2 of the gap 17. In a fifth embodiment shown in FIG. 8, the difference in height between the hole side wall 21a and the outer wall 21b corresponds to the spacing G2 of the gap 17. The spacing G2 of the gap 17 is not particularly limited, but if it is too large, a larger amount of sealant 44 is required to fill the gap 17 between the aluminum alloy plate 22 and the steel plate 1. If the spacing G2 is too small, it becomes difficult to ensure the thickness of the sealant 44. Therefore, it is preferable to design the aluminum alloy plate 22 so that the spacing G2 of the gap 17 is 0.1 mm or more and 2.0 mm or less. The recess 21 and protrusion 22b of the aluminum alloy plate 22 can be easily formed by press working or the like, and can also be formed simultaneously with the first through hole 22a.

[0074] In the first to fifth embodiments, the first plate material is a steel plate, and the second plate material having the first through hole is an aluminum alloy plate. However, in the present invention, the materials of the first and second plate materials are not particularly limited. The first plate material can be either an aluminum or aluminum alloy plate or a steel plate, and the second plate material can be the other. When the first plate material is an aluminum or aluminum alloy plate, using a welding wire made of aluminum or an aluminum alloy makes it possible to form a weld metal having the same main component as the first plate material, and similarly to the first to fifth embodiments, high joint strength can be obtained. Note that when the first plate material is an aluminum or aluminum alloy plate, an element made of aluminum or an aluminum alloy can also be used. However, because the aluminum alloy element is almost completely melted by welding, the cross-sectional shape of the resulting joint will be substantially the same as when no element is used.

[0075] Furthermore, although the first to fifth embodiments have been described above as examples in which a welding wire having the same main component as the steel plate 1, which is the first plate material, is used, the present invention may use any method that can form a weld metal having the same main component as the first plate material. For example, in addition to a gas-shielded arc welding method that uses a welding wire as a consumable electrode to obtain a weld metal having the same main component as the first plate material, a gas tungsten arc welding method that uses a welding material as a filler to obtain a weld metal having the same main component as the first plate material, or a plasma arc welding method that uses a welding material as a filler to obtain a weld metal having the same main component as the first plate material can also be applied to the present invention.

[0076] In the first to fifth embodiments, the preferred range of the gap G1 of the gap 7 is as described above, but in the present invention, the gap G1 of the gap 7 can be designed depending on the required bonding strength. A method for designing the gap G1 of the gap 7 will be described in detail below.

[0077] First, the steel sheet 1 and the aluminum alloy sheet 2 were overlapped so as to form gaps 7 with various intervals G1, and the steel sheet 1 and the aluminum alloy sheet 2 were joined using the method according to the first embodiment of the present invention, and the diameters of the formed back bead and the nugget diameter were measured. FIG. 9 is a graph showing the relationship between the nugget diameter and the back bead diameter, with the nugget diameter on the vertical axis and the back bead diameter on the horizontal axis. Then, the relationship between the diameter U1 of the back bead 12 and the nugget diameter N1 was measured, and as shown in FIG. 9, it was shown that as the diameter U1 of the back bead 12 increases, the nugget diameter N1 also increases.

[0078] Next, the joining strength was measured when the various nugget diameters were obtained. Fig. 10 is a graph showing the relationship between tensile shear strength (TSS) and nugget diameter, with the vertical axis representing tensile shear strength and the horizontal axis representing nugget diameter. As shown in Fig. 10, it was shown that the tensile shear strength of the joining portion between the steel plate 1 and the aluminum alloy plate 2 improved as the nugget diameter increased.

[0079] From these facts, it can be seen that the diameter U1 of the back bead 12 can be changed by, for example, varying the gap G1 of the gap 7 shown in Fig. 2 , and that the tensile shear strength improves in proportion to the diameter U1 of the back bead 12. Therefore, in the step of forming the weld metal 5, the back side of the steel sheet 1, i.e., the surface opposite to the surface facing the aluminum alloy sheet 2, is melted to form the back bead 12, and the size of the back bead 12 is measured, and the bonding strength between the steel sheet 1 and the aluminum alloy sheet 2 is also measured, thereby making it possible to determine the relationship between the size of the back bead 12 and the bonding strength. In other words, the bonding strength between the steel sheet 1 and the aluminum alloy sheet 2 can be predicted based on the gap G1 of the gap 7 between them.

[0080] A method for carrying out a preliminary welding test to design the gap G1 of the gap 7 according to the required joint strength will be described in more detail below. The preliminary welding test in the welding method according to the first embodiment will be described below with reference to FIGS. 1A to 1C and 2.

[0081] For the preliminary welding test, first, a first plate material for preliminary testing (steel plate 1) and a second plate material for preliminary testing (aluminum alloy plate 2) having a through hole are prepared. Next, the preliminary welding test is performed using the same method as the actual welding method. In this embodiment, since this is a preliminary welding test for the welding method according to the first embodiment, as shown in FIGS. 1A and 1B, a spacer 3 is placed between the first plate material for preliminary testing and the second plate material for preliminary testing, and then the two are placed one on top of the other. In addition, an element 4 is inserted into the through hole (first through hole 2a).

[0082] Then, as shown in FIG. 1C, element arc spot welding is performed under the same conditions as in the first embodiment. At this time, as shown in FIG. 2, the backside of the first preliminary test plate is melted to form the backside ridge 12. The size of the backside ridge 12, e.g., diameter U1, is then measured, and the joint strength, e.g., tensile shear strength, between the second preliminary test plate and the first preliminary test plate is measured. This type of preliminary welding test is performed multiple times with the preliminary test gap (gap 7) set at various intervals to determine the relationship between the spacing of the preliminary test gap and the joint strength. Then, based on the determined relationship between the size of the preliminary test gap and the joint strength, the spacing of the preliminary test gap is selected to achieve the required joint strength. The selected spacing of the preliminary test gap is then used as the spacing G1 of the gap 7, and the joining method according to the first embodiment is performed. This method allows the desired joint strength to be obtained.

[0083] Next, a welded joint of dissimilar metal materials joined by the method for joining dissimilar metal materials according to the present invention will be described.

[0084] [Joints of dissimilar metals] First Embodiment A joined joint 20 according to the first embodiment is a joint obtained by the method for joining dissimilar metal materials according to the first embodiment. As shown in FIG. 2 , the joined joint 20 according to this embodiment includes a steel plate 1 (first plate), an aluminum alloy plate 2 (second plate) having a first through hole 2a, an element 4 having a second through hole 4a inserted into the first through hole 2a, and a weld metal 5 formed inside the first through hole 2a, including a part of the steel plate 1 and a part of the element 4. The element 4 and the weld metal 5 have the same main components as the steel plate 1, and the shape of the element 4 is as described above. A gap 7 is formed by separating the steel plate 1 and the aluminum alloy plate 2 at least around the weld metal 5 between the steel plate 1 and the aluminum alloy plate 2, and the gap G1 is 0.1 mm or more and 2.0 mm or less. In this embodiment, a spacer for forming the gap 7 is disposed in a part of the region between the steel plate 1 and the aluminum alloy plate 2 excluding the periphery of the weld metal 5.

[0085] The welded joint 20 according to the first embodiment configured as described above is obtained by arranging the spacer 3 so that the gap G1 between the steel plate 1 and the aluminum alloy plate 2 is 0.1 mm or more and 2.0 mm or less, and performing element arc spot welding. Therefore, the welded joint 20 has a sufficiently large reverse wave 12, and the nugget diameter N1 at the joining interface between the steel plate 1 and the aluminum alloy plate 2 is also large, resulting in high joining strength.

[0086] <Second embodiment> A welded joint according to the second embodiment is a joint obtained by the method for joining dissimilar metal materials according to the second embodiment, and has a weld metal reinforcement formed in place of the head of the element 4 in the welded joint 20 shown in Fig. 2. Specifically, as shown in Fig. 4, the welded joint according to this embodiment has a steel plate 1 (first plate), an aluminum alloy plate 2 (second plate) having a first through hole 2a, and a weld metal 15 that includes a part of the steel plate 1, fills the first through hole 2a, and has a reinforcement 15a with a diameter larger than the first through hole 2a on the upper surface of the aluminum alloy plate 2, i.e., the surface opposite to the surface facing the steel plate 1, and has the same main composition as the steel plate 1. At least around the weld metal between the steel plate 1 and the aluminum alloy plate 2, a gap 7 is formed by separating the steel plate 1 and the aluminum alloy plate 2, and the gap G1 is 0.1 mm or more and 2.0 mm or less. In this embodiment, similarly to the first embodiment, a spacer 3 for forming a gap 7 is arranged in a part of the region between the steel plate 1 and the aluminum alloy plate 2 excluding the periphery of the weld metal.

[0087] The welded joint according to the second embodiment configured as described above is obtained by arranging the spacer 3 so that the gap G1 between the steel plate 1 and the aluminum alloy plate 2 at the welded portion is 0.1 mm or more and 2.0 mm or less, and then performing arc spot welding. Therefore, the welded joint according to the second embodiment has a sufficiently large back wave and high joining strength.

[0088] <Third embodiment> The welded joint according to the third embodiment is a joint obtained by the method for joining dissimilar metal materials according to the third embodiment, and differs from that of the first embodiment in the shape of the aluminum alloy plate of the welded joint. Other parts are the same as the welded joint according to the first embodiment shown in FIG. 2 , and therefore detailed description will be omitted. As shown in FIG. 6 , in the third embodiment, in a region between the steel plate 1 and the aluminum alloy plate 22, excluding the periphery of the weld metal, the aluminum alloy plate 22 has a protrusion 22b that protrudes toward the steel plate 1. Therefore, a gap 7 is formed in the region where the protrusion 22b is not formed, and the gap distance G1 of the gap 7 is 0.1 mm or more and 2.0 mm or less.

[0089] The welded joint according to the third embodiment configured as described above is obtained by forming a convex portion 22b on the aluminum alloy plate 22 so that the gap G1 between the steel plate 1 and the aluminum alloy plate 22 at the welded portion is 0.1 mm or more and 2.0 mm or less, and then performing arc spot welding. Therefore, the welded joint according to the third embodiment has a sufficiently large reverse wave and high joining strength.

[0090] As described above, in the present invention, the steel plate 1 (first plate material) may be provided with a convex portion that protrudes toward the aluminum alloy plate 22 (second plate material). Also, as long as a reinforcement having a diameter larger than that of the first through hole 22a is formed on the surface of the aluminum alloy plate 22 opposite to the joining surface with the steel plate 1, the element 4 may or may not be arranged.

[0091] <Fourth embodiment> The welded joint according to the fourth embodiment is a joint obtained by the method for joining dissimilar metal materials according to the fourth embodiment, and differs from the third embodiment in the shape of the aluminum alloy plates of the welded joint. Other parts are similar to the welded joint according to the third embodiment, so detailed description will be omitted. As shown in FIG. 7 , in the fourth embodiment, a first through hole 32a is provided in the aluminum alloy plate 32, and a recess 32b having a shape spaced apart from the steel plate 1 is provided in the region including the first through hole 32a. Therefore, a gap 7 is formed in the region where the recess 32b is formed, and the gap 7 has a distance G1 of 0.1 mm or more and 2.0 mm or less.

[0092] The bonded joint according to the fourth embodiment configured in this manner has a sufficiently large back wave and high bonding strength, similar to the third embodiment.

[0093] As described above, in the present invention, the steel plate 1 may be provided with a recess that is shaped to be spaced apart from the aluminum alloy plate 32. As in the third embodiment, the element 4 may or may not be arranged as long as the weld metal has a reinforcement of an appropriate shape.

[0094] <Fifth embodiment> The bonded joint according to the fifth embodiment is a joint obtained by the method for joining dissimilar metal materials according to the fifth embodiment, and the shape of the aluminum alloy plate of the bonded joint is different from that of the third embodiment. Other parts are the same as those of the bonded joint according to the third embodiment, so detailed description will be omitted. As shown in FIG. 8 , in the fifth embodiment, an aluminum alloy plate 22 is provided with a first through hole 22a and a convex portion 22b that protrudes toward the steel plate 1. Furthermore, on the opposite side of the convex portion 22b from the first through hole 22a, a concave portion 21 that surrounds the convex portion 22b is provided. The concave portion 21 is composed of a hole side wall portion 21a on the first through hole side and an outer wall portion 21b that faces the hole side wall portion 21a, and is designed so that the hole side wall portion 21a is higher than the outer wall portion 21b. Therefore, a gap 7 having a gap G1 of 0.1 mm or more and 2.0 mm or less is formed on the first through-hole 22a side of the protrusion 22b.

[0095] The bonded joint according to the fifth embodiment configured in this manner has a sufficiently large back rib and high bonding strength, as in the third embodiment. In addition, a sealant can be placed on the side of the protrusion 22b opposite to the first through hole 22a.

[0096] In the present invention, the steel plate 1 may be provided with a convex portion that protrudes toward the aluminum alloy plate 32 and a concave portion that surrounds the convex portion. As in the third embodiment, the element 4 may or may not be provided as long as the weld metal has an appropriate shape of reinforcement.

[0097] In the welded joint of dissimilar metal materials according to the present invention, as explained in the above-mentioned method for joining dissimilar metal materials, the materials of the first plate material and the second plate material having the first through hole are not particularly limited, and the first plate material can be either an aluminum or aluminum alloy plate or a steel plate, and the second plate material can be the other. When the first plate material is an aluminum or aluminum alloy plate, the weld metal is made of aluminum or an aluminum alloy. Note that when the first plate material is an aluminum or aluminum alloy plate, an element made of aluminum or an aluminum alloy may be included.

[0098] As described above in detail, in the present invention, if a gap is formed between the first plate material and the second plate material in the area where the arc is generated, the arc can be widened without increasing the diameter of the first through hole, thereby improving the joining strength.

[0099] Fig. 11 is a perspective view showing a combination of dissimilar metal materials in which a steel plate 42 having a hat-shaped cross section is placed on a flat aluminum alloy plate 41 as a first plate material. As shown in Fig. 11, a rib 43 extending in the longitudinal direction is formed on the steel plate 42, and the cross section thereof has a hat-shaped cross section. In addition, a plurality of first through holes 42a are formed on both sides of the rib 43.

[0100] When the steel plate 42, which is the second plate material, has the shape shown in Fig. 11, the diameter of the first through hole 42a cannot be designed to be large. Therefore, by providing a gap with a distance of 0.1 mm or more and 2.0 mm or less between the aluminum alloy plate 41 and the steel plate 42 around the first through hole 42a, high joining strength can be obtained. In this way, the method for joining dissimilar metal materials according to this embodiment is suitable for cases where joining in a narrow area is required. [Example]

[0101] Examples of the arc spot welding method for joining dissimilar materials according to this embodiment will be specifically described below in comparison with comparative examples.

[0102] (Example No. 1) As shown in FIGS. 1A to 1C and 2 , an aluminum alloy plate 2 having a first through hole 2a was placed on the upper surface of a steel plate 1 via a spacer 3, and an element 4 having a second through hole 4a was inserted into the first through hole 2a. In Examples 1 to 6, a 0.1 mm-thick, annular shim plate with a central hole was used as the spacer 3. One shim plate was placed around the periphery of the first through hole 2a so that the gap 7 between the steel plate 1 and the aluminum alloy plate 2 had a distance G1 of 0.1 mm. Subsequently, element arc spot welding was performed to melt a portion of the steel plate 1 to form a back bead 12, melt a portion of the element 4, and fill the second through hole 4a with weld metal 5, thereby joining the steel plate 1 and the aluminum alloy plate 2. The welding conditions are shown below.

[0103] Steel plate 1: Made of 980MPa class high tensile strength steel plate, plate thickness 1.4mm Aluminum alloy plate 2: 6000 series aluminum alloy, plate thickness 2.0 mm Diameter of the first through hole 2a: 7 mm Element 4: Made of mild steel, diameter of second through hole 4a: 4.9 mm Welding wire: (Type and diameter) JIS Z3312 G59J3M1T, 1.2mm Shielding gas flow rate: 80% Ar + 20% CO2, 25 liters / min Welding current / voltage: 140A, 20V

[0104] (Examples No. 2 to No. 8) The number of shim plates was adjusted so that the gap 7 in Example No. 1 had various gaps G1 as shown below. Example No. 2: Gap G1 is 0.2 mm Example No. 3: Gap G1 is 0.3 mm Example No. 4: Gap G1 is 0.4 mm Example No. 5: Gap G1 is 0.5 mm Example No. 6: Gap G1 is 0.8 mm Example No. 7: Gap G1 is 1.4 mm Example No. 8: Gap G1 is 2.0 mm

[0105] (Comparative Example No. 1) As shown in FIG. 3 , without using a spacer 3, an aluminum alloy plate 2 was placed in contact with the upper surface of a steel plate 1 so that a gap 7 was 0 mm, and the steel plate 1 and the aluminum alloy plate 2 were joined together in the same manner as in Example No. 1.

[0106] (Comparative Example No. 2) The number of shim plates was adjusted so that the gap 7 in Example No. 1 had the following gap G1, and the steel plate 1 and the aluminum alloy plate 2 were joined in the same manner as in Example No. 1. Comparative Example No. 2: Gap G1 is 2.3 mm

[0107] After performing one to three joinings under each of the conditions of Examples 1 to 8 and Comparative Examples 1 to 2, the diameter of the backside wave was measured, and the center of the joint was cut and the nugget diameter was measured by observing the cross section. Furthermore, for one example each of the welded joints of Comparative Examples 1 and 2 and Examples 1, 7 and 8, the center part where the weld metal was formed was cut in a direction parallel to the plate thickness direction of the steel plate 1 and the aluminum alloy plate 2, and the cut surface was observed.

[0108] Fig. 12 is a graph showing the relationship between the diameter of the back ribs and the spacing G1, with the vertical axis representing the diameter of the back ribs and the horizontal axis representing the spacing G1. Fig. 13 is a graph showing the relationship between the nugget diameter and the spacing G1, with the vertical axis representing the nugget diameter and the horizontal axis representing the spacing G1. Fig. 14 is a photograph showing a cutaway view of a portion of the comparative examples and examples (comparative examples Nos. 1 and 2, and examples Nos. 1, 7, and 8).

[0109] As shown in Figures 12 to 14 above, when the gap spacing G1 is 0.1 mm or more, the diameter of the back bead and the nugget diameter are larger than in Comparative Example No. 1 in which the gap spacing G1 is 0 mm, indicating improved joint strength. Furthermore, in the range of gap G1 up to approximately 1.5 mm, the diameter of the back bead and the nugget diameter increased with an increase in the gap spacing G1. In particular, in the range of gap G1 up to 0.3 mm, the diameter of the back bead and the nugget diameter increased rapidly with an increase in the gap spacing G1. Note that, since the joint strength between the steel sheet 1 and the aluminum alloy sheet 2, for example, the tensile shear strength, is proportional to the nugget diameter, it was shown that a more stable and high joint strength can be obtained when the gap spacing G1 is 0.3 mm or more.

[0110] On the other hand, in Comparative Example No. 2 in which the gap distance G1 was greater than 2.0 mm, the arc had difficulty reaching the steel sheet 1 sufficiently, and when the welding time was extended to resolve this, the arc penetrated the steel sheet 1, resulting in poor welding. Furthermore, even when welding was possible, the diameter of the back bead became smaller. [Explanation of symbols]

[0111] 1,42 Steel plate (first plate material) 2, 22, 32, 41 Aluminum alloy plate (second plate material) 2a, 22a, 32a, 42a First through hole 3 spacers 4 Elements 4a Second through hole 5,15 Weld metal 7 Cavity 11. Arc 12 Back Wave 15a extra sheng 20 Joints 22b Convex part 32b Recess

Claims

1. a step of placing a first plate member and a second plate member made of a material different from that of the first plate member and having a first through hole on a surface perpendicular to a thickness direction of the first plate member; a step of melting a portion of the first plate material through the first through hole by arc spot welding and forming a weld metal having the same main component as the first plate material, a step of forming a gap of 0.1 mm or more and 2.0 mm or less between a region surrounding at least the first through hole on a surface of the second plate facing the first plate and a surface of the first plate facing the second plate, before the step of forming the weld metal; Before the step of forming the weld metal, inserting an element having a second through hole into the first through hole; the element has an insertion portion formed on one axial end side of the second through hole and having a diameter that allows insertion 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 the diameter of the first through hole, A method for joining dissimilar metal materials, characterized in that the step of forming the weld metal includes a step of melting a portion of the first plate material and at least a portion of the element, and forming a weld metal that fills the second through hole.

2. a step of placing a first plate member and a second plate member made of a material different from that of the first plate member and having a first through hole on a surface perpendicular to a thickness direction of the first plate member; a step of melting a portion of the first plate material through the first through hole by arc spot welding and forming a weld metal having the same main component as the first plate material, a step of forming a gap of 0.1 mm or more and 2.0 mm or less between a region surrounding at least the first through hole on a surface of the second plate facing the first plate and a surface of the first plate facing the second plate, before the step of forming the weld metal; The step of forming the void portion includes: a step of disposing a spacer between the first plate member and the second plate member at a position excluding a region that forms the gap; and placing the second plate on a surface of the first plate perpendicular to the thickness direction of the first plate, a step of placing the second plate member, wherein the gap is formed in an area where the spacer is not placed.

3. a step of placing a first plate member and a second plate member made of a material different from that of the first plate member and having a first through hole on a surface perpendicular to a thickness direction of the first plate member; a step of melting a portion of the first plate material through the first through hole by arc spot welding and forming a weld metal having the same main component as the first plate material, a step of forming a gap of 0.1 mm or more and 2.0 mm or less between a region surrounding at least the first through hole on a surface of the second plate facing the first plate and a surface of the first plate facing the second plate, before the step of forming the weld metal; The step of forming the void portion includes: forming a recess in at least one of the first plate material and the second plate material at a position including a region where the gap is to be formed, the recess having a shape spaced apart from the other plate material; and placing the second plate on a surface of the first plate perpendicular to the thickness direction of the first plate, a step of placing the second plate material, the step of forming the void portion in the region where the recess portion is formed, the method for joining dissimilar metal materials,

4. a step of placing a first plate member and a second plate member made of a material different from that of the first plate member and having a first through hole on a surface perpendicular to a thickness direction of the first plate member; a step of melting a portion of the first plate material through the first through hole by arc spot welding and forming a weld metal having the same main component as the first plate material, a step of forming a gap of 0.1 mm or more and 2.0 mm or less between a region surrounding at least the first through hole on a surface of the second plate facing the first plate and a surface of the first plate facing the second plate, before the step of forming the weld metal; The step of forming the void portion includes: forming a protrusion in a shape that protrudes toward the other plate material in a position on at least one of the first plate material and the second plate material excluding an area where the void portion is formed; and placing the second plate on a surface of the first plate perpendicular to the thickness direction of the first plate, a step of placing the second plate material, wherein the gap is formed in an area where the protrusion is not formed.

5. a step of placing a first plate member and a second plate member made of a material different from that of the first plate member and having a first through hole on a surface perpendicular to a thickness direction of the first plate member; a step of melting a portion of the first plate material through the first through hole by arc spot welding and forming a weld metal having the same main component as the first plate material, a step of forming a gap of 0.1 mm or more and 2.0 mm or less between a region surrounding at least the first through hole on a surface of the second plate facing the first plate and a surface of the first plate facing the second plate, before the step of forming the weld metal; In the step of forming the weld metal, the first plate material is melted up to a surface opposite to the surface facing the second plate material to form a back bead, After the step of forming the weld metal, the size of the back wave is measured, and the joining strength between the second plate material and the first plate material is measured, and a relationship between the size of the back wave and the joining strength is obtained. A method for joining dissimilar metal materials, characterized in that the joining strength is predicted based on the spacing of a gap between the second plate material and the first plate material.

6. a step of placing a first plate member and a second plate member made of a material different from that of the first plate member and having a first through hole on a surface perpendicular to a thickness direction of the first plate member; a step of melting a portion of the first plate material through the first through hole by arc spot welding and forming a weld metal having the same main component as the first plate material, a step of forming a gap of 0.1 mm or more and 2.0 mm or less between a region surrounding at least the first through hole on a surface of the second plate facing the first plate and a surface of the first plate facing the second plate, before the step of forming the weld metal; A first plate material for preliminary testing and a second plate material for preliminary testing having a through hole are prepared; Before the step of forming the weld metal, a step of forming a preliminary test gap between the first plate material for preliminary test and the second plate material for preliminary test, and conducting a preliminary welding test in the same manner as the step of forming the weld metal; The preliminary welding test involves a process of melting the first preliminary test plate material up to the surface opposite to the surface facing the second preliminary test plate material to form a back rib, and a process of measuring the size of the back rib and measuring the joint strength between the first preliminary test plate material and the second preliminary test plate material, the process being carried out multiple times with the preliminary test gaps set at different intervals to determine the relationship between the spacing of the preliminary test gaps and the joint strength, A method for joining dissimilar metal materials, characterized in that a spacing of the preliminary test gap that will result in the required joining strength is selected based on the relationship, and then a step of forming a gap of the selected spacing is carried out.

7. 7. The method for joining dissimilar metal materials according to claim 2, wherein in the step of forming the weld metal, the first through hole is filled and a weld metal having a diameter larger than a diameter of the first through hole is formed on an upper surface of the second plate material, thereby joining the first plate material and the second plate material.

8. 2. The method for joining dissimilar metal materials according to claim 1, wherein in the step of forming the weld metal, a surface of the second plate material facing the first plate material and a surface of the element facing the first plate material are substantially flush with each other.

9. The first plate material is either an aluminum or aluminum alloy plate, or a steel plate, and the second plate material is the other. The joining method of dissimilar metal materials according to any one of claims 1 to 6.

10. A first plate material; a second plate member having a first through hole; a weld metal including a portion of the first plate, filling the first through hole, and having a weld metal with a diameter larger than the first through hole on a surface of the second plate opposite to a surface facing the first plate, a gap is formed by separating the first plate material and the second plate material at least around the periphery of the weld metal between the first plate material and the second plate material, and the distance between the gap parts is 0.1 mm or more and 2.0 mm or less; A joint of dissimilar metal materials, characterized in that a spacer is disposed between the first plate material and the second plate material in an area excluding at least the gap and the weld metal.

11. A first plate material; a second plate member having a first through hole; an element having a second through hole inserted into the first through hole; a weld metal formed inside the second through hole, the weld metal including a portion of the first plate material and a portion of the element; the element has an insertion portion formed on one axial end side of the second through hole and having a diameter that allows insertion 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 the diameter of the first through hole, a gap is formed between the first plate material and the second plate material at least around the periphery of the weld metal, and the gap has a spacing of 0.1 mm or more and 2.0 mm or less.

12. A first plate material; a second plate member having a first through hole; a weld metal including a portion of the first plate, filling the first through hole, and having a weld metal with a diameter larger than the first through hole on a surface of the second plate opposite to a surface facing the first plate, a gap is formed by separating the first plate material and the second plate material at least around the periphery of the weld metal between the first plate material and the second plate material, and the distance between the gap parts is 0.1 mm or more and 2.0 mm or less; A welded joint of dissimilar metal materials, characterized in that a recess having a shape that separates it from the other plate material is formed in at least one of the first plate material and the second plate material in a region that includes at least the gap portion and the weld metal.

13. A first plate material; a second plate member having a first through hole; a weld metal including a portion of the first plate, filling the first through hole, and having a weld metal with a diameter larger than the first through hole on a surface of the second plate opposite to a surface facing the first plate, a gap is formed by separating the first plate material and the second plate material at least around the periphery of the weld metal between the first plate material and the second plate material, and the distance between the gap parts is 0.1 mm or more and 2.0 mm or less; A joint of dissimilar metal materials, characterized in that a convex portion protruding toward the other plate material is formed on at least one of the first plate material and the second plate material in an area excluding at least the gap portion and the weld metal.

14. The protrusion is formed on the second plate member so as to surround the first through hole, a recessed portion having a shape spaced apart from the first plate member and surrounding the protruding portion is formed in a region on the opposite side of the protruding portion from the first through hole, the recess has a hole side wall portion on the first through hole side and an outer wall portion facing the hole side wall portion, 14. The joint of dissimilar metal materials according to claim 13, wherein the hole side wall portion is higher than the outer wall portion.

15. 14. A joint of dissimilar metal materials as described in claim 13, characterized in that a sealant that fills the gap between the first plate material and the second plate material is provided in the region opposite the first through hole with respect to the convex portion.

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