Spot-welded member and method for manufacturing spot-welded member

Abstract

A spot welding member according to one embodiment of the present disclosure comprises: a first metal plate and a second metal plate disposed on the surfaces of a spot welding member; a first internal metal plate group configured from one or more internal metal plates disposed between the first metal plate and the second metal plate; a first spot welding part for joining the first metal plate and the first internal metal plate group; and a second spot welding part for joining the second metal plate and the first internal metal plate group. An indentation of the first spot welding part is provided to the first metal plate and the one or more internal metal plates, and an indentation of the second spot welding part is provided to the first metal plate and the second metal plate. The indentation of the first spot welding part is set apart from the indentation of the second spot welding part. A first nugget is set apart from the second metal plate, and a second nugget is set apart from the first metal plate.

Description

[Technical Field]

[0001] The present invention relates to a spot-welded component and a method for manufacturing the spot-welded component. This application claims priority based on Japanese Patent Application No. 2023-137103, filed on August 25, 2023, the contents of which are incorporated herein by reference. [Background technology]

[0002] Spot welding is a resistance welding technique in which overlapping base metals are clamped between the tips of electrodes, and a current is passed through them while applying pressure, causing the metals to melt and join with the Joule heat generated. In lap resistance welding such as spot welding, the molten and solidified part that forms at the weld is called a nugget.

[0003] Spot welding is highly efficient and is used to manufacture a variety of mechanical structural parts. For example, thousands of spot welds are formed per automobile. However, spot welding presents a problem in that welding defects are likely to occur in sheet assemblies with a large sheet thickness ratio. A sheet assembly is a group of multiple stacked metal sheets that are the target of spot welding. The sheet thickness ratio of a sheet assembly is the total thickness of the metal sheets in the assembly divided by the thickness of the thinner metal sheet located on the surface of the assembly.

[0004] The nugget that joins the metal plates is formed in or near the center of the sheet assembly. If the nugget diameter is small or if the nugget is formed away from the thin sheets on the surface of the sheet assembly, the nugget and the thin sheets on the surface of the sheet assembly will not overlap, resulting in poor joining of these thin sheets. In particular, in sheet assemblies with a sheet thickness ratio of more than 6.0, poor joining of the thin sheets on the surface of the sheet assembly is more likely to occur.

[0005] Poor joints in spot welding are particularly problematic in the manufacture of automobile parts. Automobile parts are typically made up of thin mild steel sheets that form the exterior and high-strength steel sheets that form the frame. When spot welding such parts, the thin sheet that forms the exterior is inevitably placed on the outermost surface of the assembly.

[0006] Furthermore, in spot welding between high-strength steel sheets and mild steel, nuggets tend to be formed disproportionately on the high-strength steel sheets. This is because high-strength steel sheets contain more alloying elements than mild steel, and these alloying elements increase the electrical resistance of the high-strength steel sheets. In spot welding between high-strength steel sheets and mild steel, resistance heating occurs preferentially in the high-strength steel sheets, which have higher electrical resistance. Therefore, in spot welding between high-strength steel sheets and mild steel, the nugget does not grow to the mild steel sheets, which may result in poor joining of the mild steel.

[0007] Thus, poor joints are likely to occur in resistance spot welding of sheet assemblies with thin mild steel sheets on the outermost surface. It is generally believed that poor joints are particularly likely to occur in sheet assemblies with a sheet thickness ratio of more than 6.0. Poor joints are likely to occur in spot welding of three or more overlapping steel sheets. Poor joints are particularly likely to occur when the number of overlapping steel sheets is four or more.

[0008] Reducing the sheet thickness ratio to avoid poor joints reduces the design freedom of mechanical structural components. To avoid poor joints, notches can be formed in the steel sheets at the joint to reduce the number of steel sheets in the joint. However, this method reduces the strength of the component. Therefore, a technology to prevent poor joints in spot welding of sheet assemblies with a high sheet thickness ratio and three or more metal sheets is desired.

[0009] Patent Document 1 discloses a resistance spot welding method in which a pair of electrodes is used to sandwich a plate assembly in which a thinner steel plate is placed on at least one of two or more overlapping thick steel plates, and resistance spot welding is performed while applying pressure.The method comprises a preliminary step and a main step, in which a high electrode pressure is applied in the preliminary step to eliminate gaps in the plate assembly, and then in the main step, welding is performed at a low pressure, for a short time, and with a high current in the early stage of welding, and then welding is performed at a high pressure in the later stage of welding.

[0010] Patent Document 2 discloses a resistance spot welding method in which a plate assembly, consisting of two or more overlapping thick plates and a thin plate overlapping at least one of them, is sandwiched between a pair of electrodes and a pressing force is applied, and the method comprises: once the pressing force reaches a set value P, a preliminary current is started at a low current; once all of the overlapping plates are in contact with each other, the position of the electrodes is fixed, and then main current is started; by fixing the electrode position, thermal expansion of the plate assembly after the start of main current is suppressed, thereby increasing the pressing force, and setting the set pressing force P and maximum pressing force Pm to satisfy Pm≧1.5×P and P≦4kN.

[0011] Patent Document 3 discloses a resistance spot welding method for high-strength thin steel sheets, which comprises: sandwiching two or more overlapping high-strength thin steel sheets between a pair of electrodes and applying a pressure while performing resistance spot welding; after welding a first point, the position of the electrodes is moved; and after the welded portion of the first point has cooled to a temperature below the Mf point, a second weld is performed so as to partially overlap the welded portion of the first point.

[0012] Patent Document 4 discloses a spot welding method for spot welding a stack formed by stacking three or more workpieces, the spot welding method comprising the steps of: clamping the stack between a first welding tip and a second welding tip; and electrically connecting an inner workpiece, which is one of two workpieces having the greatest contact resistance and faces the inside of the stack, to an earth electrode or an electrode of the same polarity as the second welding tip that is adjacent to the inner workpiece and faces the outside of the stack; causing a current to flow from the first electrode tip to the second welding tip, thereby generating a current from the first electrode tip to the electrode via the inner workpiece, and pressing the stack with a first pressing force by the first welding tip and the second welding tip to join the inner workpiece to another workpiece; and pressing the stack with a second pressing force greater than the first pressing force to join the inner workpiece to the outer workpiece. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-241112 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-290098 [Patent Document 3] Japanese Patent Application Laid-Open No. 2010-172945 [Patent Document 4] Japanese Patent Application Laid-Open No. 2012-71333 Summary of the Invention [Problem to be solved by the invention]

[0014] In the techniques of Patent Documents 1 to 4, it is necessary to increase the welding current value to promote nugget growth and avoid poor joints. However, increasing the welding current value makes expulsion more likely to occur. Explosion refers to the phenomenon in which the base material is locally overheated and melts and splashes during lap resistance welding such as spot welding, or the metal itself. A large amount of expulsion deteriorates welding workability. Furthermore, if expulsion occurs, deep dents may form in the welded portion, reducing joint strength. With the techniques of Patent Documents 1 to 4, it is difficult to avoid both poor joints and expulsion.

[0015] In view of the above circumstances, the present invention aims to provide a spot-welded component with high strength reliability that can avoid both poor joining and the occurrence of expulsion when spot welding a plate assembly having three or more metal plates, and a method for manufacturing a spot-welded component. [Means for solving the problem]

[0016] The gist of the present invention is as follows.

[0017] (1) A spot-welded component according to one embodiment of the present disclosure comprises: one first metal plate and one second metal plate arranged on a surface of the spot-welded component; a first internal metal plate group consisting of one or more internal metal plates arranged between the first metal plate and the second metal plate; a first spot weld having a first nugget joining the first metal plate and the first internal metal plate group; and a second spot weld having a second nugget joining the second metal plate and the first internal metal plate group, wherein an indentation of the first spot weld is provided on the first metal plate and the internal metal plate, an indentation of the second spot weld is provided on the first metal plate and the second metal plate, the indentation of the first spot weld is separated from the indentation of the second spot weld, the first nugget is separated from the second metal plate, and the second nugget is separated from the first metal plate. (2) Preferably, in the spot-welded member described in (1) above, the number of the inner metal plates constituting the first inner metal plate group to which the first nugget is joined is two or more. (3) Preferably, the spot-welded component described in (1) or (2) above has a second internal metal plate group consisting of one or more internal metal plates arranged between the first internal metal plate group and the second metal plate, the first nugget is spaced apart from the second internal metal plate group, and the second nugget joins the second metal plate, the first internal metal plate group, and the second internal metal plate group. (4) Preferably, in the spot-welded member described in any one of (1) to (3) above, the distance between the center of the indentation of the first spot weld and the center of the indentation of the second spot weld is 10 mm or more and 50 mm or less in plan view. (5) Preferably, in the spot-welded member according to any one of (1) to (4) above, the second metal plate is thicker than the first metal plate. (6) Preferably, in the spot-welded component described in (5) above, the value obtained by dividing the total thickness of the first metal plate and the first internal metal plate group to which the first nugget is joined by the thickness of the first metal plate is less than 6.0, and the value obtained by dividing the total thickness of the first metal plate, the second metal plate, and the internal metal plate possessed by the spot-welded component by the thickness of the first metal plate is more than 6.5. (7) Preferably, in the spot-welded component described in any one of (1) to (6) above, the first metal plate, the second metal plate, and the internal metal plate are steel plates, the Vickers hardness of the first metal plate is 150 HV or less, and the hardness of at least one of the second metal plate and the internal metal plate is 300 HV or more. (8) Preferably, in the spot-welded component according to any one of (1) to (7) above, an adhesive is provided at one or more joint interfaces. (9) Preferably, in the spot-welded component described in any one of (1) to (8) above, the number of metal plates to which the second nugget is joined is three or more, and the value obtained by dividing the total thickness of the metal plates to which the second nugget is joined by the thickness of the second metal plate is 1.8 to 4.2.

[0018] (10) A method for manufacturing a spot-welded component according to another aspect of the present disclosure includes the steps of: performing a first spot welding on a first internal metal plate group consisting of a stacked first metal plate and one or more internal metal plates to form a joined body having a first nugget that joins the first metal plate and the first internal metal plate group; and performing a second spot welding on the internal metal plate arranged on the surface of the joined body to form a second nugget that joins the first internal metal plate group and the second metal plate of the joined body; wherein the welding point of the second spot welding is separated from the welding point of the first spot welding, and the second spot welding is terminated before the second nugget grows to the first metal plate. (11) Preferably, in the method for manufacturing a spot-welded component described in (10) above, the number of the internal metal plates constituting the first internal metal plate group to be subjected to the first spot welding is two or more. (12) Preferably, in the manufacturing method of spot-welded components described in (10) or (11) above, a second internal metal plate group consisting of one or more internal metal plates and the second metal plate are stacked in order on the internal metal plate arranged on the surface of the joined body, and the second spot welding is performed. (13) Preferably, in the method for manufacturing a spot-welded component described in any one of (10) to (12) above, the distance between the center of the welding point in the first spot welding and the center of the welding point in the second spot welding is 10 mm or more and 50 mm or less in plan view. (14) Preferably, in the method for manufacturing a spot-welded component according to any one of (10) to (13) above, the second metal plate is thicker than the first metal plate. (15) Preferably, in the manufacturing method of spot-welded components described in (14) above, the value obtained by dividing the total thickness of the first metal plate and the first internal metal plate group of the joined body by the thickness of the first metal plate is less than 6.0, and the value obtained by dividing the total thickness of the first metal plate, the second metal plate, and the internal metal plate of the spot-welded component by the thickness of the first metal plate is more than 6.5. (16) Preferably, in the manufacturing method of spot-welded components described in any one of (10) to (15) above, the first metal plate, the second metal plate, and the internal metal plate are steel plates, the Vickers hardness of the first metal plate is 150 HV or less, and the hardness of at least one of the second metal plate and the internal metal plate is 300 HV or more. (17) Preferably, the method for manufacturing a spot-welded component described in any one of (10) to (16) above further includes a step of applying an adhesive to one or more of the surface of the first metal plate and the surface of the internal metal plate before the first spot welding, and the surface to which the adhesive is applied is the joining interface of the joined body. (18) Preferably, the method for manufacturing a spot-welded member described in any one of (10) to (17) above further includes a step of applying an adhesive to one or more of the surfaces of the joined body and the surfaces of the metal plates to be placed on top of the joined body before the second spot welding, and the surfaces to which the adhesive is applied form the joining interface of the spot-welded member. (19) Preferably, in the manufacturing method of spot-welded components described in any one of (10) to (18) above, the number of metal plates to which the second nugget is joined is 3 or more, and the value obtained by dividing the total thickness of the metal plates to which the second nugget is joined by the thickness of the second metal plate is 1.8 to 4.2. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a spot-welded component with high strength reliability that can avoid both poor joining and the occurrence of expulsion when spot welding a plate assembly having three or more metal plates, and a method for manufacturing a spot-welded component. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a cross-sectional schematic view of a first spot welding of two metal plates and a joined body. FIG. [Figure 2] 2 is a cross-sectional view schematically illustrating the joined body of FIG. 1, a second spot weld to one metal plate, and a spot-welded member. FIG. [Figure 3] 1 is a cross-sectional schematic view of a first spot welding of three metal plates and a joined body. FIG. [Figure 4] 4 is a cross-sectional view showing the joined body of FIG. 3, a second spot weld to one metal plate, and a spot-welded member. FIG. [Figure 5A] 2 is a cross-sectional view showing the joined body of FIG. 1, a second spot weld to two metal plates, and a spot-welded member. FIG. [Figure 5B] 2 is a cross-sectional view showing the joined body of FIG. 1, a second spot weld to three metal plates, and a spot-welded member. FIG. [Figure 6] FIG. 1 is a cross-sectional view of a spot-welded member in which surface expulsion has occurred. [Figure 7A] 10 is a cross-sectional photograph of a spot-welded member of Example 3. [Figure 7B] 1 is a cross-sectional photograph of a spot-welded member of Example 4. [Figure 8] 1 is a cross-sectional photograph of an example of a spot-welded component having five metal plates. DETAILED DESCRIPTION OF THE INVENTION

[0021] (1. Method for manufacturing spot-welded member 1) A manufacturing method of a spot-welded member 1 according to one embodiment of the present invention includes the steps of: performing a first spot weld S1 on a first internal metal plate group 1131 consisting of one stacked first metal plate 111 and one or more internal metal plates 113 to form a joint 13 having a first nugget 121 that joins the first metal plate 111 and the first internal metal plate group 1131; and performing a second spot weld S2 to overlap a second metal plate 112 on the internal metal plate 113 arranged on the surface of the joint 13 to form a second nugget 122 that joins the first internal metal plate group 1131 and the second metal plate 112 of the joint 13; separating the welding point WP of the second spot weld S2 from the welding point WP of the first spot weld S1, and terminating the second spot weld S2 before the second nugget 122 grows to the first metal plate 111.

[0022] (First spot welding S1) First, a plate assembly is prepared by stacking one or more internal metal plates 113 on a first internal metal plate group 1131, and then stacking one first metal plate 111 on top of the first internal metal plate group 1131. A first spot weld S1 is then performed on this plate assembly. In spot welding, the stacked metal plates are sandwiched between the tips of a pair of spot welding electrodes E, and a current is passed through the plates while applying pressure. Indirect spot welding, which is resistance welding in which the metal plates are not sandwiched between the tips of the pair of electrodes E, is not considered spot welding in the manufacturing method of the spot-welded member 1 according to this embodiment. The metal sheets are melted by Joule heat generated by the current. The molten zone grows from near the center of the sheet assembly toward the surface of the sheet assembly. The sheet assembly is the multiple metal sheets stacked together to be spot welded. When the current is stopped, heat transfer occurs from the metal sheets to electrode E, causing the molten metal to solidify. The nugget formed by the solidification of the molten metal joins the metal sheets.

[0023] The first metal plate 111 is part of the multiple metal plates that the spot-welded component 1 has. The internal metal plate 113 that constitutes the first internal metal plate group 1131 is also part of the multiple metal plates that the spot-welded component 1 has. The first metal plate 111 is arranged on the surface of the spot-welded component 1. The internal metal plate 113 is arranged inside the spot-welded component 1. However, when the first spot welding S1 is completed, the internal metal plate 113 is arranged on the surface of the joined body 13.

[0024] Note that the spot-welded member 1 may have a second internal metal plate group 1132 composed of one or more internal metal plates 113 (see FIGS. 5A and 5B). The first internal metal plate group 1131 and the second internal metal plate group 1132 are distinguished based on whether or not they are the target of the first spot welding S1. The first internal metal plate group 1131 is the target of the first spot welding S1. Therefore, a first nugget 121 is formed in the first internal metal plate group 1131. On the other hand, the second internal metal plate group 1132 is not the target of the first spot welding S1. Therefore, a first nugget 121 is not formed in the second internal metal plate group 1132. In other words, the second internal metal plate group 1132 is separated from the first nugget 121. The second internal metal plate group 1132 will be described in detail later.

[0025] The first spot welding S1 forms a joined body 13 as shown in FIG. 1 and other drawings. The joined body 13 has a first metal plate 111 and an internal metal plate 113 stacked together, and a first nugget 121. The first metal plate 111 is disposed on one surface of the joined body 13. At the end of the first spot welding S1, the internal metal plate 113 is disposed on the surface of the joined body 13. The first nugget 121 joins the first metal plate 111 and a first internal metal plate group 1131.

[0026] A first indentation 1211 is formed on the surface of the joined body 13 by the first spot welding S1. That is, the first indentation 1211 is formed on the first metal plate 111 and the internal metal plate 113 disposed on the surface of the joined body 13. The indentation is a depression on the surface of the base material caused by the electrode tip as a result of spot welding.

[0027] (Second spot welding S2) Next, one second metal plate 112 is placed on the internal metal plate 113 disposed on the surface of the joined body 13 (see FIG. 2, etc.). A second spot weld S2 is applied to the joined body 13 and the second metal plate 112 that have been placed on top of each other. A second nugget 122 is formed by the second spot weld S2, thereby obtaining a spot-welded member 1 as shown in FIG. 2, etc.

[0028] The second metal plate 112 is one of the multiple metal plates of the spot-welded member 1. The second metal plate 112 is disposed on the surface of the spot-welded member 1 opposite to the first metal plate 111.

[0029] The spot-welded member 1 has a first metal plate 111, a second metal plate 112, an inner metal plate 113, a first nugget 121, and a second nugget 122. Since the first spot weld S1 is not applied to the second metal plate 112, the second metal plate 112 is spaced apart from the first nugget 121.

[0030] The second spot weld S2 forms second indentations 1221 on both surfaces of the spot-welded member 1. That is, the first metal plate 111 and the second metal plate 112 are provided with second indentations 1221.

[0031] The second nugget 122 joins the first inner metal plate group 1131 of the joined body 13 and the second metal plate 112. However, the second spot welding S2 is terminated before the second nugget 122 grows to the first metal plate 111. Therefore, the second nugget 122 does not join all of the metal plates of the spot-welded member 1. The second nugget 122 is separated from the first metal plate 111.

[0032] In the second spot weld S2, the weld point WP of the second spot weld S2 is spaced apart from the weld point WP of the first spot weld S1. The weld point WP is a location on the metal plate where the spot welding electrode E comes into contact. By spaced apart the weld point WP of the first spot weld S1 and the weld point WP of the second spot weld S2, the second nugget 122 is spaced apart from the first nugget 121. By observing the cross section of the spot-welded member 1, it can be determined whether the first nugget 121 is spaced apart from the second nugget 122.

[0033] (Action and effect) In the first spot welding S1, only a portion of the metal plates included in the spot-welded member 1 are welded. As a result, in the first spot welding S1, the plate thickness ratio of the plate assembly is reduced. The plate thickness ratio of the plate assembly is the value obtained by dividing the total thickness of the metal plates in the plate assembly by the thickness of the thinner metal plate located on the surface of the plate assembly. By creating a plate assembly from only a portion of the metal plates, the total thickness of the plate assembly can be reduced, and the plate thickness ratio can be reduced.

[0034] Reducing the sheet thickness ratio in the first spot weld S1 reduces the welding current value required to grow the first nugget 121 to the first metal sheet 111. Reducing the sheet thickness ratio makes it possible to avoid poor joining of the first metal sheet 111. Furthermore, reducing the sheet thickness ratio also makes it possible to reduce the welding current value and avoid expulsion in the first spot weld S1.

[0035] In the second spot welding S2, all of the metal plates included in the spot-welded member 1 appear to be welded. However, in the second spot welding S2, the second nugget 122 is not grown to the first metal plate 111. Because the first metal plate 111 is joined to the first inner metal plate group 1131 in the first spot welding S1, there is no need in the second spot welding S2 to grow the second nugget 122 to the first metal plate 111. Therefore, in the second spot welding S2, a lower welding current value can be selected than in spot welding of a typical plate assembly with a high plate thickness ratio.

[0036] Increasing the welding current value to grow the nugget to the first metal sheet 111 increases the risk of surface expulsion occurring on the surface of the second metal sheet 112. Surface expulsion is a phenomenon in which molten metal from the nugget erupts from the surface of a metal sheet (see FIG. 6). Surface expulsion protrudes from the surface of the weld or adheres to the surface of the metal sheet, damaging the appearance of the spot-welded member 1. Surface expulsion also impairs welding workability. However, the manufacturing method for the spot-welded member 1 according to this embodiment can extremely efficiently suppress expulsion during the second spot weld S2.

[0037] Furthermore, in the second spot weld S2, the weld point WP of the second spot weld S2 is separated from the weld point WP of the first spot weld S1. This makes it possible to suppress current shunting in the second spot weld S2. Current shunting refers to current flowing in a parallel circuit formed by existing weld points in spot welding. In the second spot weld S2, the first nugget 121 becomes an existing weld point that causes current shunting. If current shunting to an existing weld point occurs, the current flowing through the second metal sheet increases, further increasing the risk of surface expulsion occurring on the surface of the second metal sheet 112.

[0038] In the method for manufacturing the spot-welded member 1 according to this embodiment, the welding point WP of the second spot weld S2 is separated from the welding point WP of the first spot weld S1 to suppress shunting. By suppressing shunting, the occurrence of expulsion at the second spot weld S2 is further reliably suppressed.

[0039] The above has described the most basic aspect of the method for manufacturing the spot-welded member 1 according to this embodiment. A more preferred aspect will now be described.

[0040] (Spot welding of four or more metal plates) 1, the number of internal metal plates 113 constituting the first internal metal plate group 1131 subjected to the first spot welding S1 may be one. On the other hand, as shown in FIGS. 3 and 4, the number of internal metal plates 113 constituting the first internal metal plate group 1131 subjected to the first spot welding S1 may be two or more. In this case, one internal metal plate 113 is disposed on the surface of the joined body 13, and the remaining internal metal plates 113 are disposed inside the joined body 13.

[0041] As shown in FIG. 2, the second spot welding S2 may be performed after only the second metal plate 112 is placed on the internal metal plate 113 arranged on the surface of the joined body 13. In this case, the second metal plate 112 is directly placed on the internal metal plate 113 arranged on the surface of the joined body 13. On the other hand, as shown in FIGS. 5A and 5B, the second spot welding S2 may be performed after a second internal metal plate group 1132 consisting of one or more internal metal plates 113 and the second metal plate 112 are placed on the internal metal plate 113 arranged on the surface of the joined body 13. That is, a second internal metal plate group 1132 consisting of another internal metal plate 113 may be placed between the second metal plate 112 and the first internal metal plate group 1131 of the joined body 13. In FIG. 5A, the second internal metal plate group 1132 includes one internal metal plate 113. 5B, the number of internal metal plates 113 included in the second internal metal plate group 1132 is two. The number of internal metal plates 113 included in the second internal metal plate group 1132 may be three or more.

[0042] 5A and 5B, the second metal plate 112 is overlapped with the first internal metal plate group 1131 included in the joined body 13 via the additionally provided second internal metal plate group 1132. Then, a second spot weld S2 is applied to the joined body 13, the second internal metal plate group 1132, and the second metal plate 112.

[0043] 3, 4, 5A, and 5B, the number of metal plates included in the spot-welded component 1 can be set to four or more. This makes it possible to manufacture a complex spot-welded component 1 having a large number of metal plates.

[0044] 5A and 5B, the number of metal plates included in the joined body 13 is two. On the other hand, as illustrated in Fig. 3, the number of metal plates included in the joined body 13 may be three or more, and two or more metal plates may be spot-welded to the joined body 13 as illustrated in Fig. 5A and 5B.

[0045] (Center distance between welding points WP) The distance between the weld point WP of the first spot weld S1 and the weld point WP of the second spot weld S2 is not particularly limited. From the viewpoint of further reducing shunt current and more reliably suppressing expulsion, it is preferable that the distance D between the center of the weld point WP of the first spot weld S1 and the center of the weld point WP of the second spot weld S2 be 10 mm or more, 15 mm or more, 20 mm or more, or 30 mm or more in a plan view. On the other hand, from the viewpoint of further improving the load transmission efficiency of the spot-welded member 1, it is preferable that the distance D between the center of the weld point WP of the first spot weld S1 and the center of the weld point WP of the second spot weld S2 be 50 mm or less, 45 mm or less, 40 mm or less, or 35 mm or less in a plan view.

[0046] The center of the welding point WP is the location where the central axis of the electrode E was located during spot welding. The center of the first indentation 1211 formed on the surface of the joined body 13 is considered to be the center of the welding point WP in the first spot weld S1. The center of the second indentation 1221 formed on the surface of the spot-welded member 1 is considered to be the center of the welding point WP in the second spot weld S2.

[0047] In manufacturing the spot-welded member 1, the first spot weld S1 and the second spot weld S2 may each be performed two or more times. For example, if the metal plate is a flange portion of a hat-shaped member, the first spot weld S1 and the second spot weld S2 are performed multiple times on the flange portion along the extension direction of the flange portion. In this case, the distance D between the center of the weld point WP of the first spot weld S1 and the center of the weld point WP of the second spot weld S2 means the distance D between the center of the weld point WP of the first spot weld S1 and the center of the weld point WP of the second spot weld S2 that is closest to it.

[0048] (Thickness of second metal plate 112) The thickness of the second metal plate 112 is not particularly limited. From the viewpoint of reliably joining the second metal plate 112 to at least the adjacent internal metal plate 113, it is preferable that the second metal plate 112 be thicker than the first metal plate 111. This makes it easier to grow the second nugget 122 up to the second metal plate 112. The thickness of the second metal plate 112 may be 1.1 times or more, 1.2 times or more, 1.5 times or more, or 2.0 times or more the thickness of the first metal plate 111.

[0049] (plate thickness ratio) The sheet thickness ratio of the joined body 13, i.e., the value obtained by dividing the total thickness of the first metal plate 111 and the first inner metal plate group 1131 of the joined body 13 by the thickness of the first metal plate 111, is preferably less than 6.0. This makes it easier to grow the first nugget 121 up to the first metal plate 111. The sheet thickness ratio of the joined body 13 may be 5.8 or less, 5.5 or less, or 5.0 or less.

[0050] The plate thickness ratio of the spot-welded component 1 based on the thickness of the first metal plate 111, i.e., the value obtained by dividing the total thickness of the first metal plate 111, the second metal plate 112, and the inner metal plate 113 of the spot-welded component 1 by the thickness of the first metal plate 111, is preferably greater than 6.5. This further improves the strength and rigidity of the spot-welded component 1. The plate thickness ratio of the spot-welded component 1 based on the thickness of the first metal plate 111 may also be 6.8 or more, 7.0 or more, 7.2 or more, or 7.5 or more. When the number of metal plates joined to the second nugget 122 is three or more, the plate thickness ratio for the second nugget 122 is preferably 1.8 to 4.2. The number of metal plates joined to the second nugget 122 is the total number of second metal plates 112 and internal metal plates 113 joined to the second nugget 122. When specifying the number of metal plates joined to the second nugget 122, it is not taken into consideration whether the internal metal plate 113 belongs to the first internal metal plate group 1131 or the second internal metal plate group 1132. The plate thickness ratio for the second nugget 122 is the value obtained by dividing the total thickness of the metal plates joined to the second nugget 122 by the thickness of the second metal plate 112. In order to ensure that the number of metal plates joined by the second nugget 122 is three or more, the number of internal metal plates 113 constituting the first internal metal plate group 1131 may be two or more, as shown in FIG. 4. In the spot-welded member 1 illustrated in FIG. 4, the number of internal metal plates 113 constituting the first internal metal plate group 1131 is two, and the number of internal metal plates 113 constituting the second internal metal plate group 1132 is zero. The second nugget 122 in FIG. 4 joins the two internal metal plates 113 of the first internal metal plate group 1131 and the second metal plate 112. Therefore, the number of metal plates joined by the second nugget 122 in FIG. 4 is three. On the other hand, in order to ensure that the number of metal plates joined by the second nugget 122 is three or more, the number of internal metal plates 113 constituting the second internal metal plate group 1132 may be one or more, as shown in FIG. 5A. In the spot-welded member 1 illustrated in FIG. 5A, the number of internal metal plates 113 constituting the first internal metal plate group 1131 is one, and the number of internal metal plates 113 constituting the second internal metal plate group 1132 is one. The second nugget 122 in FIG. 5A joins one internal metal plate 113 included in the first internal metal plate group 1131, one internal metal plate 113 included in the second internal metal plate group 1132, and the second metal plate 112. Therefore, the number of metal plates joined by the second nugget 122 in FIG. 5A is also three. In either case, the thickness ratio for the second nugget 122 is preferably 1.8 to 4.2. By setting the thickness ratio for the second nugget 122 to 1.8 or more, the occurrence of surface expulsion from the second metal plate 112 can be further suppressed. Furthermore, by setting the thickness ratio for the second nugget 122 to 4.2 or less, the bond between the second nugget 122 and the adjacent internal metal plate can be further strengthened. When the thickness of the second metal plate is increased, the cross-sectional area through which current flows increases, and the electrical resistance decreases. As a result, the shunt current to the first nugget side increases. For this reason, if the current value is constant, the second nugget is not sufficiently formed. Normally, the current is increased to compensate for this, which makes surface expulsion more likely to occur. The thickness ratio of the second nugget 122 may be set to 2.0 or more, 2.5 or more, or 3.0 or more. The thickness ratio of the second nugget 122 may be set to 4.0 or less, 3.5 or less, or 3.2 or less.

[0051] (Type of metal plate) The type of metal plate is not particularly limited. In the manufacturing method of the spot-welded member 1 according to this embodiment, any material that can be spot-welded can be used as the welding base material. A suitable material can be used depending on the application of the spot-welded member 1. Examples of metal plates include steel plates, aluminum plates, and stainless steel plates.

[0052] A suitable example of the metal plate is a steel plate. In particular, it is preferable that one or more of the metal plates be high-strength steel plates. For example, if the spot-welded component 1 is an automobile part, by using one or more of the metal plates as high-strength steel plates, the thickness of the metal plates can be reduced while ensuring the strength of the spot-welded component 1. By reducing the thickness of the metal plates, the weight of the spot-welded component 1 can be reduced.

[0053] When the metal plates are steel plates, it is preferable that the first metal plate 111 be made of mild steel, and that one or more of the second metal plate 112 and the inner metal plate 113 be made of high-strength steel. For example, it is preferable that the Vickers hardness of the first metal plate 111 be 150 HV or less, 140 HV or less, 130 HV or less, or 120 HV or less, and that the hardness of one or more of the second metal plate 112 and the inner metal plate 113 be 300 HV or more, 320 HV or more, 380 HV or more, or 440 HV or more. The first metal plate 111 is disposed on the outermost surface of the spot-welded member 1, and is therefore suitable, for example, for use as an exterior component of an automobile. By using thin mild steel for the first metal plate 111, it is possible to improve the formability of the first metal plate 111 and enhance the aesthetic appearance of the automobile. Furthermore, from the viewpoint of improving the corrosion resistance of automobiles, zinc-based plated steel sheets (electrogalvanized steel sheets, hot-dip galvanized steel sheets, galvannealed hot-dip galvanized steel sheets, zinc-nickel plated steel sheets) are desirable. The second metal sheet 112 and the internal metal sheet 113 are suitable for, for example, automobile frame components. By using a high-strength steel sheet for one or more of the second metal sheet 112 and the internal metal sheet 113, the collision safety of the automobile can be improved. Examples of high-strength steel sheets include press-formed cold-rolled steel sheets, hot-rolled steel sheets, and hot-stamped steel sheets. In the case of automobile body parts requiring corrosion resistance, zinc-based plated steel sheets (hot-dip galvanized steel sheets, galvannealed hot-dip galvanized steel sheets, zinc-based plated hot-stamped steel sheets) and aluminum-based plated hot-stamped steel sheets may be included.

[0054] (Application of adhesive) Weld bonding may be applied to the manufacturing method of the spot-welded member 1 according to this embodiment. Weld bonding is a method in which an adhesive is applied to the joint interface 14 in advance and then spot welding is performed. Therefore, the manufacturing method of the spot-welded member 1 according to this embodiment may include a step of bonding the metal plates using an adhesive, in addition to the first spot welding S1 and the second spot welding S2. By using both bonding and spot welding, the rigidity and joint strength of the spot-welded member 1 can be further increased. Weld bonding may be applied to either the first spot welding S1 or the second spot welding S2, or to both.

[0055] For example, the manufacturing method of the spot-welded member 1 may further include a step of applying an adhesive to one or more of the surface of the first metal plate 111 and the surface of the inner metal plate 113 before the first spot welding S1. In this case, the surface to which the adhesive is applied is defined as the joining interface 14 of the joined body 13. The joining interface 14 of the joined body 13 refers to the mating surfaces of the overlapping metal plates in the joined body 13.

[0056] For example, the manufacturing method of the spot-welded member 1 may further include a step of applying an adhesive to one or more of the surfaces of the joined body 13 and the surfaces of the metal plates that are to be placed on the joined body 13 before the second spot welding S2. In this case, the surface to which the adhesive is applied is referred to as the joint interface 14 of the spot-welded member 1. The joint interface 14 of the spot-welded member 1 refers to the mating surfaces of the overlapping metal plates in the spot-welded member 1.

[0057] The spot-welded member 1 has two or more bonding interfaces 14. From the viewpoint of improving rigidity and bonding strength, it is preferable to provide an adhesive at at least one bonding interface 14. For example, it is preferable to provide an adhesive at the bonding interface 14 between the first metal plate 111 and the second metal plate 112, and it is even more preferable to provide an adhesive at all bonding interfaces 14. The type of adhesive is not particularly limited. Examples of adhesives include a thermosetting epoxy adhesive, urethane adhesive, or rubber adhesive that hardens during heat treatment (140°C to 190°C) used in electrodeposition coating of automobiles.

[0058] (2. Spot welding material 1) A spot-welded member 1 according to another embodiment of the present invention includes a first metal plate 111 and a second metal plate 112 arranged on the surface of the spot-welded member 1, a first internal metal plate group 1131 consisting of one or more internal metal plates 113 arranged between the first metal plate 111 and the second metal plate 112, a first spot weld having a first nugget 121 joining the first metal plate 111 and the first internal metal plate group 1131, and a second nugget 122 joining the second metal plate 112 and the first internal metal plate group 1131. and a second spot weld formed on the inner metal plate 113, wherein a first indentation 1211 of the first spot weld is formed on the first metal plate 111 and the inner metal plate 113, and a second indentation 1221 of the second spot weld is formed on the first metal plate 111 and the second metal plate 112, the indentation of the first spot weld being spaced apart from the indentation of the second spot weld, the first nugget 121 being spaced apart from the second metal plate 112, and the second nugget 122 being spaced apart from the first metal plate 111. The spot-welded component 1 according to this embodiment will be described in detail below. The preferred aspects of the method for manufacturing the spot-welded component 1 described above can also be applied to the spot-welded component 1 according to this embodiment.

[0059] 2 and other figures, the spot-welded member 1 has a first metal plate 111, a second metal plate 112, and an internal metal plate 113. The first metal plate 111 and the second metal plate 112 are disposed on the surface of the spot-welded member 1. The internal metal plate 113 is disposed between the first metal plate 111 and the second metal plate 112.

[0060] As shown in Fig. 2 and other figures, the spot-welded member 1 further includes a first spot-welded portion having a first nugget 121 and a second spot-welded portion having a second nugget 122. The spot-welded portion is a general term that includes the nugget and the heat-affected zone (HAZ). The spot-welded portion also has an indentation (i.e., a depression on the surface of the base material caused by the electrode tip).

[0061] The first nugget 121 joins the first metal plate 111 to the first inner metal plate group 1131. The second nugget 122 joins the second metal plate 112 to the first inner metal plate group 1131.

[0062] The first nugget 121 and the second nugget 122 are distinguished based on their corresponding indentations. One of the first indentations 1211, i.e., the indentation of the first spot weld, is provided on the surface of the spot-welded component 1, and the other is provided inside the spot-welded component 1. The second indentations 1221, i.e., the indentations of the second spot weld, are both provided on the surface of the spot-welded component 1. By observing the appearance of the spot-welded component 1, it is possible to identify areas where indentations are provided on both surfaces and areas where indentations are provided on only one surface. The nugget located at the area where indentations are provided on only one surface of the spot-welded component 1 is the first nugget 121. The nugget located at the area where indentations are provided on both surfaces of the spot-welded component 1 is the second nugget 122.

[0063] The first metal plate 111 and the second metal plate 112 are distinguished based on the nuggets provided thereon. The metal plate on which the first nugget 121 is provided is the first metal plate 111. The metal plate on which the second nugget 122 is provided is the second metal plate 112. In other words, the first indentation 1211 is provided on the first metal plate 111 and the internal metal plate 113 constituting the first internal metal plate group 1131, and the second indentation 1221 is provided on the first metal plate 111 and the second metal plate 112. Note that, when observing the appearance of the spot-welded component 1, it can be seen that the number of indentations differs between the first surface and the second surface of the spot-welded component 1. It can be determined that the metal plate with the most indentations is the first metal plate 111.

[0064] The first indentation 1211 (i.e., the indentation of the first spot weld) is spaced apart from the second indentation 1221 (i.e., the indentation of the second spot weld). By observing the surface of the first metal plate 111, the outer edge of the first indentation 1211 and the outer edge of the second indentation 1221 can be easily identified. Therefore, whether the first indentation 1211 and the second indentation 1221 are spaced apart from each other can be easily determined based on an external observation of the spot-welded member 1. Alternatively, whether the first indentation 1211 and the second indentation 1221 are spaced apart from each other may be determined by observing a cross section of the nugget. A method for observing the cross section will be described later.

[0065] 2 and other drawings, the first nugget 121 is spaced apart from the second metal plate 112. The second nugget 122 is spaced apart from the first metal plate 111. That is, both the first nugget 121 and the second nugget 122 join only some of the multiple metal plates included in the spot-welded member 1.

[0066] (Action and effect) The first nugget 121 is spaced apart from the second metal plate 112. Similarly, the second nugget 122 is spaced apart from the first metal plate 111. That is, the first nugget 121 and the second nugget 122 join only some of the metal plates included in the spot-welded member 1. Therefore, a high welding current is not required to manufacture the first nugget 121 and the second nugget 122, and expulsion is suppressed. The first nugget 121 and the second nugget 122 can be manufactured easily.

[0067] Furthermore, poor welding can be avoided when manufacturing the first nugget 121 and the second nugget 122. Generally, when joining a sheet assembly with a high sheet thickness ratio, it is difficult to grow the nugget up to the thinnest metal sheet arranged on the surface of the sheet assembly. Therefore, poor welding is likely to occur in the thinnest metal sheet arranged on the surface of the sheet assembly. However, when manufacturing the first nugget 121, the second metal sheet 112 is not the welding target, and the sheet thickness ratio is reduced. When manufacturing the second nugget 122, there is no need to grow the nugget up to the first metal sheet 111, and therefore the sheet thickness ratio is substantially reduced. Therefore, the first nugget 121 can reliably join the first metal sheet 111 and the adjacent metal sheet. Furthermore, the second nugget 122 can reliably join the second metal sheet 112 and the adjacent metal sheet.

[0068] In addition, because the first indentation 1211 and the second indentation 1221 are spaced apart, shunting is suppressed during the second spot weld S2. By suppressing shunting, expulsion during the second spot weld S2 is more reliably suppressed.

[0069] The most basic aspect of the spot-welded member 1 according to this embodiment has been described above. A more preferred aspect will now be described.

[0070] (Number of metal plates to be joined by the first nugget 121 and the second nugget 122) The first nugget 121 joins the first metal plate 111 and a first internal metal plate group 1131. In the spot-welded member 1 illustrated in FIGS. 2, 5A, and 5B, the first nugget 121 joins the first metal plate 111 and one internal metal plate 113. Therefore, the first internal metal plate group 1131 includes one internal metal plate 113, and the number of metal plates joined by the first nugget 121 is two. On the other hand, as illustrated in FIG. 4, the first nugget 121 may join the first metal plate 111 and two or more internal metal plates 113. That is, the number of internal metal plates 113 that make up the first internal metal plate group 1131 may be two or more, and the number of metal plates may be three or more.

[0071] The second nugget 122 joins the second metal plate 112 and the first internal metal plate group 1131. In the spot-welded member 1 illustrated in FIG. 2, the second nugget 122 joins the second metal plate 112 and one internal metal plate 113. Therefore, the first internal metal plate group 1131 includes one internal metal plate 113, and the number of metal plates joined by the second nugget 122 is two. On the other hand, as illustrated in FIG. 4, the second nugget 122 may join the second metal plate 112 and two or more internal metal plates 113. That is, the number of internal metal plates 113 that make up the first internal metal plate group 1131 may be two or more, and the number of metal plates may be three or more.

[0072] 5A and 5B, a second internal metal plate group 1132 including one or more internal metal plates 113 that are not joined to the first nugget 121 but are joined to the second nugget 122 may be disposed between the first internal metal plate group 1131 and the second metal plate 112. As shown in FIG. 5A, the number of internal metal plates 113 included in the second internal metal plate group 1132 may be one. On the other hand, as shown in FIG. 5B, similar to the first internal metal plate group 1131, the number of internal metal plates 113 that constitute the second internal metal plate group 1132 may also be two or more. In this case, the first indentation 1211 provided in the internal metal plate 113 is provided in the internal metal plate 113 of the first internal metal plate group 1131 that is adjacent to the second internal metal plate group 1132. Therefore, the first internal metal plate group 1131 and the second internal metal plate group 1132 can be distinguished from each other based on the positions of the first nugget 121 and the second nugget 122 and the position of the first indentation 1211 formed on the internal metal plate 113.

[0073] By making the number of metal plates joined by the first nugget 121 and / or the second nugget 122 three or more, and making the number of metal plates included in the spot-welded component 1 four or more, it becomes possible to manufacture a complex spot-welded component 1 having a large number of metal plates.

[0074] (Center-to-center spacing of indentations) In the spot-welded member 1 according to this embodiment, the distance D between the center of the first indentation 1211 (i.e., the indentation of the first spot welded portion) and the center of the second indentation 1221 (i.e., the indentation of the second spot welded portion) is not particularly limited. From the viewpoint of further reducing shunting and more reliably suppressing expulsion, it is preferable that the distance D between the center of the first indentation 1211 and the center of the second indentation 1221 be 10 mm or more, 15 mm or more, 20 mm or more, or 30 mm or more in a plan view. On the other hand, from the viewpoint of further improving the load transmission efficiency of the spot-welded member 1, it is preferable that the distance D between the center of the first indentation 1211 and the center of the second indentation 1221 be 50 mm or less, 45 mm or less, 40 mm or less, or 35 mm or less in a plan view.

[0075] (Thickness of second metal plate 112) There are no particular limitations on the thickness of the second metal plate 112. From the viewpoint of reliably joining the second metal plate 112 to the internal metal plate 113, it is preferable that the second metal plate 112 be thicker than the first metal plate 111. The thickness of the second metal plate 112 may be 1.1 times or more, 1.2 times or more, 1.5 times or more, or 2.0 times or more the thickness of the first metal plate 111.

[0076] (plate thickness ratio) The value obtained by dividing the total thickness of the first metal plate 111 and the first internal metal plate group 1131 to which the first nugget 121 is joined by the thickness of the first metal plate 111 is preferably less than 6.0, 5.8 or less, 5.5 or less, or 5.0 or less. This makes it easier to grow the first nugget 121 up to the first metal plate 111.

[0077] The plate thickness ratio of the spot-welded component 1 based on the thickness of the first metal plate 111, i.e., the value obtained by dividing the total thickness of the first metal plate 111, the second metal plate 112, and the inner metal plate 113 of the spot-welded component 1 by the thickness of the first metal plate 111, is preferably greater than 6.5. This further improves the strength and rigidity of the spot-welded component 1. The plate thickness ratio of the spot-welded component 1 based on the thickness of the first metal plate 111 may also be 6.8 or more, 7.0 or more, 7.2 or more, or 7.5 or more. As illustrated in FIGS. 4, 5A, and 5B, when the number of metal plates to which the second nugget 122 is joined is three or more, the value obtained by dividing the total thickness of the metal plates to which the second nugget 122 is joined by the thickness of the second metal plate 112 is preferably 1.8 to 4.2. The value obtained by dividing the total thickness of the metal plates to which the second nugget 122 is joined by the thickness of the second metal plate 112 is referred to as the thickness ratio of the second nugget 122. By setting the thickness ratio of the second nugget 122 to 1.8 or more, the occurrence of surface expulsion from the second metal plate 112 can be further suppressed. Furthermore, by setting the thickness ratio of the second nugget 122 to 4.2 or less, the joining between the second nugget 122 and the adjacent internal metal plate can be further strengthened. The thickness ratio of the second nugget 122 may be 2.0 or more, 2.5 or more, or 3.0 or more. The thickness ratio of the second nugget 122 may be 4.0 or less, 3.5 or less, or 3.2 or less.

[0078] (Type of metal plate) As explained with respect to the manufacturing method of the spot-welded member 1, the type of metal plate is not particularly limited. A suitable example of the metal plate is a steel plate. When the first metal plate 111, the second metal plate 112, and the internal metal plate 113 are steel plates, the Vickers hardness of the first metal plate 111 is preferably 150 HV or less, 140 HV or less, 130 HV or less, or 120 HV or less, and the hardness of one or more of the second metal plate 112 and the internal metal plate 113 is 300 HV or more, 320 HV or more, 350 HV or more, or 380 HV. There is no particular upper limit for the hardness of the first metal plate 111, the second metal plate 112, and the internal metal plate 113; however, the hardness of these metal plates may be, for example, 730 HV or less or 700 HV or less.

[0079] (glue) An adhesive may be provided at one or more joint interfaces 14 of the spot-welded component 1. The joint interfaces 14 of the spot-welded component 1 refer to the mating surfaces of the overlapping metal plates in the spot-welded component 1. This further increases the rigidity and joint strength of the spot-welded component 1. From the viewpoint of improving the rigidity and joint strength, it is preferable to provide an adhesive at at least one joint interface 14. For example, it is preferable to provide an adhesive at the joint interface 14 between the first metal plate 111 and the second metal plate 112, and it is even more preferable to provide an adhesive at all of the joint interfaces 14.

[0080] Although the embodiment of the present invention has been described above, the present invention is not limited thereto and can be modified as appropriate without departing from the technical spirit of the invention. A more preferred example of a spot-welded member 1 according to this embodiment and a method for manufacturing the same will be described below. The preferred embodiment described below is applicable to both the spot-welded member 1 and the method for manufacturing the same.

[0081] (Tensile strength of metal plate) Spot welding is widely used in the manufacture of automobile parts. Therefore, the manufacturing method of the spot-welded member 1 according to this embodiment may be applied to automobile parts. In this case, for example, the first metal plate 111 is an exterior automobile part that requires high workability. The other metal plates are automobile frame parts that require high strength. Therefore, the tensile strength of the first metal plate 111 may be 440 MPa or less, 420 MPa or less, or 400 MPa or less, and the tensile strength of one or more metal plates other than the first metal plate 111 may be 980 MPa or more, 1180 MPa or more, or 1470 MPa or more. This facilitates the processing of automobile exterior parts and ensures the strength of automobile frame parts.

[0082] (Surface treatment of metal plates) One or more metal sheets may have a surface treatment layer. The surface treatment layer may be, for example, a plating layer. The composition of the plating layer may be suitable for the composition of the underlying metal sheet. For example, when the metal sheet is a steel sheet, the plating layer may be, for example, a zinc-based plating layer or an aluminum-based plating layer. The zinc-based plating layer is a plating layer having an average Zn content of 30% by mass or more, or 50% by mass or more. Examples include electrogalvanizing, hot-dip galvanizing, galvannealed hot-dip galvanizing, zinc-nickel plating, hot-stamped galvannealed hot-dip galvanizing, zinc-nickel plating, and galvannealed hot-dip galvanizing. The aluminum-based plating layer is a plating layer having an average Al content of 20% by mass or more, or 30% by mass or more. For example, it is hot-stamped aluminum plating. A coating film may be provided on the surface of the spot-welded member 1. The coating film may be, for example, an electrodeposition coating film provided on the surface of the spot-welded member 1 after spot welding.

[0083] (Thickness of metal plate) There are no particular limitations on the thickness of the metal plates of the spot-welded member 1. For example, the thickness of the first metal plate 111 is preferably 0.50 to 1.1 mm. The thickness of the second metal plate 112 is preferably 0.9 to 2.6 mm. The thickness of the inner metal plate 113 is preferably 0.9 to 2.6 mm.

[0084] (nugget diameter) The sizes of the first nugget 121 and the second nugget 122 are not particularly specified. As long as the above requirements are met, an appropriate nugget diameter can be adopted depending on the material, thickness, number, etc. of the metal plates. For example, if the thickness of the first metal plate 111 is 0.5 mm to 1.1 mm and the total thickness of the metal plates in the spot-welded member 1 is 3.5 mm to 9.0 mm, it is preferable that the diameter of the first nugget 121 be 3√(t1) to 9√(t1) and the diameter of the second nugget 122 be 3√(t2) to 9√(t2). Here, t1 is the thickness of the first metal plate 111, and t2 is the thickness of the second metal plate 112.

[0085] Here, the diameter of the first nugget 121 refers to the width of the nugget measured on a virtual line along the joint interface 14 between the first metal plate 111 and the adjacent internal metal plate 113. The diameter of the second nugget 122 refers to the width of the nugget measured on a virtual line along the joint interface 14 between the second metal plate 112 and the adjacent internal metal plate 113. The width of the molten solidified portion is measured on a plane that includes the center of the first dent and the center of the second dent and is perpendicular to the first metal plate 111. The nugget diameter can be controlled by appropriately changing the current flow conditions depending on the material, thickness, number, etc. of the metal plates.

[0086] (Pressure welding part) In the welded portion where the second nugget 122 is provided, the first metal plate 111 and the first inner metal plate group 1131 are not joined by the second nugget 122. However, in the welded portion where the second nugget 122 is provided, it is preferable that a pressure-welded portion is provided between the first metal plate 111 and the first inner metal plate group 1131. The pressure-welded portion is a portion where the base materials are solid-state welded, but not melted or solidified. By pressure-welding the first metal plate 111 in the second spot weld S2, the joining strength of the spot-welded member 1 is further increased.

[0087] If a pressure-welded portion is provided between the first metal plate 111 and the first inner metal plate group 1131, the presence of the pressure-welded portion can be confirmed by a chisel test. In the chisel test, a chisel is driven into the interface between the first metal plate 111 and the first inner metal plate group 1131 at the spot-welded portion to fracture the joint. If a plug fracture occurs on the side of the first metal plate 111, the joint is determined to fall into one of the following situations. (1) At the joint that was subjected to the chisel test, a first nugget 121 joining the first metal plate 111 and the first inner metal plate group 1131 was formed. (2) At the joint that underwent the chisel test, a second nugget 122 and a pressure-welded portion joining the first metal plate 111 and the first inner metal plate group 1131 were formed. The fractured portion is then cut and the cross section is etched, allowing the nugget formed at the fractured portion to be observed. If the nugget is separated from the first metal plate 111, it is determined that the nugget is the second nugget 122, and that a pressure-welded portion was provided between the first metal plate 111 and the first inner metal plate group 1131.

[0088] (Welding conditions) The conditions for the first spot weld S1 and the second spot weld S2 are not particularly specified. As long as the above requirements are met, appropriate welding conditions can be adopted depending on the material, thickness, number, etc. of the metal plates. Examples of suitable welding conditions are listed below.

[0089] The first spot weld S1 and the second spot weld S2 may each be passed through a single current or multiple times (two or more times). When multiple current passes are used, the current values ​​for the first and second passes may be the same or different. For sheet thicknesses exceeding 5 mm, pulsation welding, in which current is passed multiple times at the same current value, may be used. An upslope may be applied at the start of current application, and a downslope may be applied at the end of current application. The current waveforms for these upslope and downslope currents may be continuous or pulsed. The upslope reduces the risk of expulsion and hydrogen embrittlement cracking when welding ultra-high-strength steel sheets when there is a large gap between the metal sheets or when welding galvanized hot-stamped steel sheets with high surface resistance. The downslope reduces the risk of hydrogen embrittlement cracking and LME cracking due to the galvanization when welding ultra-high-strength steel sheets.

[0090] The current value may also be changed during current application. For example, a high current may be applied in the early stages of current application and then reduced in the later stages. This promotes nugget formation. Alternatively, a low current may be applied in the early stages of current application and then increased in the later stages. This reduces the occurrence of expulsion, especially when the gap between the metal sheets is large.

[0091] The conditions of the number of times of current application, slope control, and current value during welding may be freely combined depending on the plate combination. If necessary, the pressure during welding may be changed.

[0092] The welding power source can be a DC inverter, an AC inverter, or a single-phase AC. The electrode shape can be DR, R, CR, or CF type. The electrode material can be chromium copper, chromium-zirconium copper, or alumina-dispersed copper. When welding galvanized steel sheets, if LME cracks occur at the indentation, alumina-dispersed copper is recommended as the electrode material.

[0093] In a more preferred example of welding conditions, a DR-type electrode with an electrode tip of 5 mm to 8 mm is used, the pressure is 250 kgf to 700 kgf (2.451 kN to 6.864 kN), the current time is 12 cycles to 60 cycles (240 msec to 1200 msec), the current value is 6 kA to 13 kA, and the holding time is 1 cycle to 60 cycles (20 msec to 1200 msec).

[0094] (Application) The use of the spot-welded member 1 and the manufacturing method thereof according to this embodiment is not particularly limited. For example, it is preferable to incorporate the manufacturing method of the spot-welded member 1 into the manufacturing process of an automobile part. For example, the first spot weld S1 can be applied to the side frame assembly process, and the second spot weld S2 can be applied to the body assembly process.

[0095] In this case, a side frame is first manufactured by performing a first spot weld S1 on an outer plate, which is a side panel, and a B-pillar outer, which is a reinforcement material. This side frame has a configuration similar to the joined body 13 having two metal plates shown in FIG. 1. The side panel, which is an outer plate, corresponds to the first metal plate 111 of the joined body 13, and the B-pillar outer corresponds to the first inner metal plate group 1131 of the joined body 13. Next, a body is manufactured by performing a second spot weld S2 on the side frame (joint body 13), the side sill outer, and the side sill inner. The body has a configuration similar to the spot-welded member 1 shown in FIG. 5A. The side sill outer corresponds to the second inner metal plate group 1132, and the side sill inner corresponds to the second metal plate 112.

[0096] Alternatively, a side frame may be manufactured by performing first spot welding S1 on the outer plate, the B-pillar outer, and the side sill outer. This side frame has a configuration similar to the joined body 13 having three metal plates shown in FIG. 3. The outer plate corresponds to the first metal plate 111 of the joined body 13, and the B-pillar outer and the side sill outer correspond to a first internal metal plate group 1131 of the joined body 13. The internal metal plate 113 adjacent to the first metal plate 111 is the B-pillar outer. Next, a body is manufactured by performing second spot welding S2 on the side frame (joint body 13) and the side sill inner. The body has a configuration similar to the spot-welded member 1 shown in FIG. 4. The side sill inner corresponds to the second metal plate 112.

[0097] In either example, if the outer plate is joined to the B-pillar outer by the first spot weld S1, there is no need to form a nugget at the interface between the outer plate and the B-pillar outer by the second spot weld S2. The second spot weld S2 is performed for the purpose of joining the reinforcements together.

[0098] (Evaluation method) In the spot-welded component 1, whether the first indentation 1211 is spaced apart from the second indentation 1221 can usually be easily determined by visually observing the surface of the first metal plate 111. If the outer edges of the first indentation 1211 and the second indentation 1221 are unclear, the cross sections of the first nugget 121 and the second nugget 122 are observed. By cutting the spot-welded component 1 along a plane that passes through the center of the first indentation 1211 and the center of the second indentation 1221 and is perpendicular to the first metal plate 111, and adjusting the cut surface appropriately, the cross sections of the first nugget 121 and the second nugget 122 can be visually recognized. As shown in FIG. 2 and other figures, if the first nugget 121 is spaced apart from the second nugget 122 in the cross section, the first indentation 1211 is considered to be spaced apart from the second indentation 1221. In this case, it is also considered that the welding point WP of the second spot weld S2 was separated from the welding point WP of the first spot weld S1 during the production of the spot-welded component 1.

[0099] In the spot-welded member 1, whether the first nugget 121 is separated from the second metal plate 112 is determined by observing a cross section of the first nugget 121. The spot-welded member 1 is cut along a plane that passes through the center of the first indentation 1211 and is perpendicular to the first metal plate 111, and the cut surface is appropriately adjusted, so that the cross section of the first nugget 121 can be visually confirmed. If the second metal plate 112 is not melted and not incorporated into the first nugget 121, it is determined that the first nugget 121 is separated from the second metal plate 112.

[0100] In the spot-welded component 1, whether the second nugget 122 is separated from the first metal plate 111 is determined by observing a cross section of the second nugget 122. The cross section of the second nugget 122 can be visually observed by cutting the spot-welded component 1 along a plane that passes through the center of the second indentation 1221 and is perpendicular to the first metal plate 111, and adjusting the cut surface appropriately. If the first metal plate 111 is not melted and not incorporated into the second nugget 122, it is determined that the second nugget 122 is separated from the first metal plate 111. In this case, it is determined that the second spot welding S2 was completed in the manufacture of the spot-welded component 1 before the second nugget 122 grew to the first metal plate 111.

[0101] The distance D between the center of the first indentation 1211 and the center of the second indentation 1221 can be easily measured by visually observing and identifying the centers of the surfaces of the first metal plate 111. Furthermore, the distance D between the center of the first indentation 1211 and the center of the second indentation 1221 is considered to be the same as the distance D between the center of the weld point WP in the first spot weld S1 and the center of the weld point WP in the second spot weld S2.

[0102] The thicknesses of the first metal plate 111, the second metal plate 112, and the inner metal plate 113 are measured at locations sufficiently distant from the first nugget 121 and the second nugget 122. Specifically, the locations where no deformation due to the first spot weld S1 and the second spot weld S2 occurs are used as the locations where the thicknesses of the metal plates are measured.

[0103] The Vickers hardness of the first metal plate 111, the second metal plate 112, and the inner metal plate 113 is measured in accordance with JIS Z 2244:2009 "Vickers hardness test - Test method." The hardness measurement is performed in locations where no deformation occurs due to the first spot weld S1 and the second spot weld S2. The hardness measurement is also performed on a cross section perpendicular to the surface of the metal plate. The indentation is made at the t / 4 position. The t / 4 position is a position where the depth from the surface of the metal plate is t / 4. t refers to the thickness of the metal plate. The test force is 0.5 kgf. Three tests are performed. The measurement points are spaced 0.5 mm apart. The arithmetic mean value of the values ​​obtained in each test is considered to be the hardness of the metal plate.

[0104] The tensile strength of the first metal plate 111, the second metal plate 112, and the inner metal plate 113 is measured in accordance with JIS Z 2241:2011 "Method of tensile testing for metallic materials." Alternatively, the tensile strength may be calculated from a Vickers hardness test. In this case, SAE J 417 is used for conversion. [Example]

[0105] The effects of one embodiment of the present invention will be explained in more detail using examples. However, the conditions in the examples are merely examples adopted to confirm the feasibility and effects of the present invention. The present invention is not limited to these examples. Various conditions may be adopted in the present invention as long as they do not deviate from the gist of the present invention and achieve the object of the present invention.

[0106] Example 1 Spot-welded components were manufactured by spot welding various sheet combinations made of materials 1 to 4 shown in Table 1. The columns "Material 1" to "Material 4" in Table 1 list the plating type and tensile strength (unit: MPa) of the steel sheet, as well as the thickness t (unit: mm), in that order. GA270: GA plated steel sheet, tensile strength 270 MPa (110 HV) GA980: GA plated steel sheet, tensile strength 980MPa (300HV) GA1180: GA plated steel sheet, tensile strength 1180MPa (390HV) GA1470: GA plated steel sheet, tensile strength 1470MPa (460HV) CR1470: Uncoated steel sheet, tensile strength 1470MPa (460HV) Al1800: Aluminum-plated hot-stamped steel sheet with a tensile strength of 1800 MPa (550 HV) GA plating refers to alloyed hot-dip galvanizing.

[0107] The plate assembly was stacked in the order of material 1, material 2, material 3, and material 4. Material 1 corresponds to the first metal plate, material 4 corresponds to the second metal plate, and materials 2 and 3 correspond to the internal metal plates. The "total thickness" listed in Table 1 is the sum of the thicknesses of materials 1 to 4 (unit: mm). The "plate thickness ratio" listed in Table 1 is the value obtained by dividing the total thickness of the plate assembly by the thickness of material 1.

[0108] [Table 1]

[0109] The plate assemblies shown in Table 1 were spot welded under the conditions shown in Table 2. For examples in which four steel plates were joined in two spot welds, the number of the metal plate to be spot welded in the first spot weld, the plate thickness ratio of the joint, the welding conditions for the first spot weld, the welding conditions for the second spot weld, and the weld point center-to-center distance are listed. The "plate thickness ratio of the joint" is the total thickness of the metal plates to be spot welded in the first spot weld divided by the thickness of material 1. The "weld point center-to-center distance" is the distance between the centers of the weld points of the first spot weld and the second spot weld. For examples in which four steel plates were joined in a single spot weld, only the welding conditions for that spot weld are listed. The welding conditions column lists the applied pressure, welding current, and welding time. One cycle was 1 / 50 seconds.

[0110] [Table 2]

[0111] The spot-welded components were subjected to a chisel test as specified in JIS Z 3144:2013, "Field Test Methods for Spot and Projection Welds." Specifically, a chisel was pressed between Material 1 and Material 2 near the first nugget, applying a tensile force in the thickness direction of the weld. This test determined whether the bond strength between Material 1 and Material 2 was satisfactory. The first nugget was fractured between Material 1 and Material 2 for each test piece by driving the chisel. The nugget diameter was then evaluated using a three-level scale in the "Chisel Test Results of the Bonding Interface Between Material 1 and Material 2" column in Table 3, based on the method described in JIS Z 3139 6.1 (Cross-Section Macro Test). The evaluation criteria were as follows: Examples rated "C" were determined to have poor bonding in Material 1. Nugget diameter is 4.25√t (t is the thickness of material 1) or more: A Nugget diameter is 3√t or more and less than 4.25√t: B Nugget diameter less than 3√t: C The second nugget was also subjected to a chisel test in the same manner as the first nugget. The plug diameters of the first and second nuggets were measured in accordance with JIS Z 3144:2013, "Field Test Methods for Spot and Projection Welds." The plug diameter refers to the average diameter of the plug-shaped fracture portion measured after a fracture test. A plug fracture refers to a button-shaped fracture within the nugget, in the heat-affected zone, or in the base metal outside the nugget. As a result, it was confirmed that the plug diameter of the first nugget in all of the present invention examples was 4.25√t or more (t is the thickness of material 1). Furthermore, it was confirmed that the plug diameter of the second nugget in all of the present invention examples was also 4.25√t or more (t is the thickness of material 4).

[0112] Thereafter, whether or not the second nugget of the spot-welded component had grown to material 1 was confirmed by cross-sectional observation. The observation was performed on a cut surface that passed through the center of the second indentation and was perpendicular to material 1. The observation results were recorded in the "Material 1 interface nugget formation in second spot welding" column. If a second nugget had formed at the interface between material 1 and material 2, "Yes" was recorded in the "Material 1 interface nugget formation in second spot welding" column, and otherwise "No" was recorded.

[0113] Furthermore, the amount of surface expulsion in Material 4 was evaluated and listed in Table 3. The occurrence of surface expulsion in the second spot weld was evaluated by cross-sectional observation. When traces of the nugget weld metal protruding toward the metal surface near the indentation in the second spot weld were confirmed, the "Surface Explosion" column was marked "NG." When minute molten spatter was confirmed only on the surface, the "Surface Explosion" column was marked "NORMAL." When the result was not judged to be either NG or NORMAL, the "Surface Explosion" column was marked "GOOD."

[0114] [Table 3]

[0115] In Examples 1 and 8, materials 1 to 4 were joined by a single spot welding. In these examples, poor joining of material 1 occurred.

[0116] In Examples 2 and 12, the welding point of the second spot weld was not spaced apart from the welding point of the first spot weld. As a result, the second spot welds in Examples 2 and 12 suffered from significant surface expulsion.

[0117] In Example 7, in the second spot welding, the second nugget was grown to Material 1. As a result, in the second spot welding of Example 7, significant surface expulsion occurred.

[0118] In other examples, materials 1 to 4 were joined by first spot welding and second spot welding, the welding point of the second spot welding was separated from the welding point of the first spot welding, and the second spot welding was terminated before the second nugget grew to the first metal plate. In these examples, there was no poor joining of material 1, and surface expulsion was sufficiently suppressed, resulting in spot-welded components with high strength reliability.

[0119] FIG. 7A is a cross-sectional photograph of the spot-welded component of Example 3. The metal plates in FIG. 7A are, from top to bottom, GA270-0.65t (material 1), GA980-1.6t (material 2), CR1470-1.6t (material 3), and CR1470-1.6t (material 4). The nugget on the right side of FIG. 7A is the first nugget, and the nugget on the left side of FIG. 7A is the second nugget. The center-to-center spacing of the weld points in the spot-welded component of FIG. 7A is 12 mm. In addition, in manufacturing the spot-welded component of FIG. 7A, the first spot welding was performed on materials 1 and 2.

[0120] 7A shows that the thin metal plate arranged at the top of the page is securely joined to the adjacent metal plate, and also shows that no surface expulsion occurred during the second spot welding.

[0121] FIG. 7B is a cross-sectional photograph of the spot-welded component of Example 4. The metal plates in FIG. 7B are, from top to bottom, GA270-0.65t (Material 1), GA980-1.6t (Material 2), CR1470-1.6t (Material 3), and CR1470-1.6t (Material 4). The nugget on the right side of FIG. 7B is the first nugget, and the nugget on the left side of FIG. 7B is the second nugget. The center-to-center spacing of the weld points in the spot-welded component of FIG. 7B was 12 mm. In addition, in manufacturing the spot-welded component of FIG. 7B, the first spot welding was performed on Materials 1, 2, and 3.

[0122] 7B shows that the thin metal plate at the top of the page is securely joined to the adjacent metal plate, and also shows that no surface expulsion occurred during the second spot welding.

[0123] (Example 2: Plate Thickness Ratio Regarding Second Nugget) Spot-welded components were manufactured by spot welding various sheet combinations made of materials 1 to 4 shown in Table 4. The columns "Material 1" to "Material 4" in Table 1 list the plating type and tensile strength (unit: MPa) of the steel sheet, as well as the thickness t (unit: mm), in that order.

[0124] The sheet assembly was stacked in the order of material 1, material 2, material 3, and material 4. Material 1 corresponds to the first metal sheet, material 4 corresponds to the second metal sheet, and materials 2 and 3 correspond to the inner metal sheets. Table 4 lists the materials targeted by the first spot welding. In addition, materials 2, 3, and 4 were joined in the second spot welding. The "sheet thickness ratio for the second nugget" in Table 4 is the value obtained by dividing the total thickness of materials 2 to 4 joined by the second nugget by the thickness of the second metal sheet (i.e., material 4). For ease of explanation, the joint shape is listed in Table 4.

[0125] [Table 4]

[0126] [Table 5]

[0127] A chisel test was performed on the spot-welded components obtained by spot welding. Specifically, a chisel was pressed into (1) between material 1 and material 2 and (2) between material 3 and material 4 near the first nugget to apply a tensile force in the thickness direction of the weld. This test determined whether the bond strength between material 1 and material 2 and the bond strength between material 3 and material 4 were satisfactory. The chisel was used to fracture the first nugget between material 1 and material 2 of each test specimen. Furthermore, the chisel was used to fracture the second nugget between material 3 and material 4 of each test specimen. The nugget diameters were evaluated using a three-level scale in the "Chisel test results of the bond interface between material 1 and material 2" column in Table 6, based on the method described in JIS Z 3139 6.1 (cross-sectional macro test). The evaluation criteria were as follows: Examples rated "C" were determined to have poor bonding in material 1. Nugget diameter is 4.25√t (t is the thickness of material 4) or more: A Nugget diameter is 3√t or more and less than 4.25√t: B Nugget diameter less than 3√t: C

[0128] Furthermore, the amount of surface expulsion in Material 4 was evaluated and listed in Table 6. The occurrence of surface expulsion in the second spot weld was evaluated by cross-sectional observation. When traces of the nugget weld metal protruding toward the metal surface near the indentation in the second spot weld were confirmed, the "Surface Explosion" column was recorded as "NG." When minute molten spatter was confirmed only on the surface, the "Surface Explosion" column was recorded as "NORMAL." When the result was not judged as either NG or NORMAL, the "Surface Explosion" column was recorded as "GOOD."

[0129] [Table 6]

[0130] In the spot-welded members of Examples A1 to A11, the number of metal plates joined by the second nugget was three or more, and the value obtained by dividing the total thickness of the metal plates joined by the second nugget by the thickness of the second metal plate was 1.8 to 4.2. In these examples, both the joining strength of the first nugget and the joining strength of the second nugget were excellent, and further, the occurrence of expulsion was suppressed. In the spot-welded component of Example A12, the number of metal plates joined by the second nugget was three or more, and the value obtained by dividing the total thickness of the metal plates joined by the second nugget by the thickness of the second metal plate was less than 1.8. In A12, surface expulsion, in which the surface melted slightly, occurred. However, since surface expulsion that would affect strength did not occur in A12, A12 is also considered an example of the invention.

[0131] (Example 3: Spot-welded component having five metal plates) The following five metal plates were spot welded together: Material 1 was the first metal plate, and Material 5 was the second metal plate. ·Material 1: GA270-0.65t ·Material 2: CR980-1.2t ·Material 3: CR980-1.2t ·Material 4: Al1800-1.6t ·Material 5: Al1800-1.6t First, a first spot welding was performed on materials 1, 2, and 3 to form a joint having a first nugget. Next, materials 4 and 5 were overlapped on material 3 of the joint, and a second spot welding was performed to form a second nugget joining materials 2, 3, 4, and 5. The welding point of the second spot welding was spaced apart from the welding point of the first spot welding. The second spot welding was terminated before the second nugget grew to the first metal plate.

[0132] A cross-sectional photograph of the spot-welded component obtained by the above-mentioned procedure is shown in Figure 8. In the spot-welded component of Figure 8, poor joining was avoided. In addition, in the spot-welded component of Figure 8, the occurrence of expulsion was also avoided. [Explanation of symbols]

[0133] S1 First spot weld S2 Second spot weld 1 Spot welding parts 111 First Metal Plate 112 Second Metal Plate 113 Internal metal plate 1131 First inner metal plate group 1132 Second inner metal plate group 121 First Nugget 1211 First Impression 122 Second Nugget 1221 Second Impression 13 Zygote 14 Bonding interface D Distance between the center of the first nugget and the center of the second nugget E-electrode WP welding point

Claims

1. A spot-welded member, a first metal plate and a second metal plate disposed on a surface of the spot-welded member; a first internal metal plate group consisting of one or more internal metal plates disposed between the first metal plate and the second metal plate; a first spot weld having a first nugget joining the first metal plate and the first inner metal plate group; a second spot weld having a second nugget joining the second metal plate and the first inner metal plate group; Equipped with an indentation of the first spot weld is provided on the first metal plate and the inner metal plate; an indentation of the second spot weld is provided on the first metal plate and the second metal plate; the indentation of the first spot weld is spaced from the indentation of the second spot weld; the first nugget is spaced from the second metal plate; the second nugget is spaced from the first metal plate; The number of the inner metal plates constituting the first inner metal plate group to which the first nugget is joined is two or more. Spot welded components.

2. a second internal metal plate group consisting of one or more internal metal plates disposed between the first internal metal plate group and the second metal plate; the first nugget is spaced apart from the second inner metal sheets; The spot-welded component of claim 1 , wherein the second nugget joins the second metal plate, the first inner metal plate group, and the second inner metal plate group.

3. 3. The spot-welded member according to claim 1, wherein a distance between a center of the indentation of the first spot weld and a center of the indentation of the second spot weld is 10 mm or more and 50 mm or less in a plan view.

4. 3. The spot-welded component according to claim 1, wherein the second metal plate is thicker than the first metal plate.

5. a value obtained by dividing the total thickness of the first metal plate and the first inner metal plate group to which the first nugget is joined by the thickness of the first metal plate is less than 6.0; The value obtained by dividing the total thickness of the first metal plate, the second metal plate, and the inner metal plate of the spot-welded member by the thickness of the first metal plate is greater than 6.

5. The spot-welded component according to claim 4.

6. the first metal plate, the second metal plate, and the inner metal plate are steel plates; The Vickers hardness of the first metal plate is 150 HV or less, At least one of the second metal plate and the internal metal plate has a hardness of 300 HV or more. The spot-welded member according to claim 1 or 2.

7. 3. The spot-welded component according to claim 1, wherein an adhesive is provided at one or more joint interfaces.

8. The number of the metal plates to which the second nugget is joined is three or more, The value obtained by dividing the total thickness of the metal plates to which the second nugget is joined by the thickness of the second metal plate is 1.8 to 4.

2. The spot-welded component according to claim 1 .

9. a step of performing first spot welding on a first group of internal metal plates, which is composed of one stacked first metal plate and one or more internal metal plates, to form a joined body having a first nugget joining the first metal plate and the first group of internal metal plates; a step of overlapping one second metal plate on the internal metal plate arranged on the surface of the joined body, and performing second spot welding to form a second nugget joining the first internal metal plate group and the second metal plate of the joined body; Equipped with spaced apart a welding point of the second spot weld from a welding point of the first spot weld; the second spot weld is terminated before the second nugget grows to the first metal sheet; The number of the inner metal plates constituting the first inner metal plate group to be subjected to the first spot welding is set to 2 or more. A method for manufacturing spot-welded components.

10. 10. The method for manufacturing a spot-welded member according to claim 9, wherein the internal metal plate arranged on the surface of the joined body is sequentially stacked with a second internal metal plate group consisting of one or more internal metal plates and the second metal plate, and the second spot welding is performed.

11. 11. The method for manufacturing a spot-welded member according to claim 9 or 10, wherein a distance between a center of a weld point in the first spot weld and a center of a weld point in the second spot weld is 10 mm or more and 50 mm or less in plan view.

12. The method for manufacturing a spot-welded component according to claim 9 or 10, wherein the second metal plate is thicker than the first metal plate.

13. The value obtained by dividing the total thickness of the first metal plate and the first internal metal plate group of the joined body by the thickness of the first metal plate is less than 6.

0. The value obtained by dividing the total thickness of the first metal plate, the second metal plate, and the internal metal plate of the spot-welded member by the thickness of the first metal plate is greater than 6.

5. The method for manufacturing a spot-welded component according to claim 12.

14. The first metal plate, the second metal plate, and the inner metal plate are steel plates; The Vickers hardness of the first metal plate is 150 HV or less, The hardness of at least one of the second metal plate and the internal metal plate is set to 300 HV or more. The method for manufacturing a spot-welded member according to claim 9 or 10.

15. The method further includes applying an adhesive to one or more of a surface of the first metal plate and a surface of the inner metal plate before the first spot welding; The surface to which the adhesive is applied is used as the bonding interface of the bonded body. The method for manufacturing a spot-welded member according to claim 9 or 10.

16. The method further includes applying an adhesive to one or more of the surface of the joined body and the surface of a metal plate to be placed thereon before the second spot welding; The surface to which the adhesive is applied is used as a joining interface of the spot-welded member. The method for manufacturing a spot-welded member according to claim 9 or 10.

17. The number of the metal plates to which the second nugget is joined is three or more, The total thickness of the metal plates to which the second nugget is joined is divided by the thickness of the second metal plate, and the value is set to 1.8 to 4.

2. The method for manufacturing a spot-welded member according to claim 9 or 10.

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