Welded joints, mechanical structural members, automotive members, and methods for manufacturing welded joints

Abstract

The present invention provides a welded joint, a mechanical structural member, an automotive member, and a method for manufacturing a welded joint, which can be easily manufactured, ensure corrosion resistance of metal plates at the mating surface, and suppress blowholes in the weld metal. [Solution] A welded joint according to one aspect of the present disclosure comprises a weld having stacked metal plates and a weld metal that joins the metal plates, wherein one or more metal plates are zinc-plated metal plates having a zinc-plated layer on one or both surfaces, the one or more zinc-plated layers are arranged on the mating surfaces of the metal plates, the boiling point of the zinc-plated layer arranged on the mating surface is lower than the melting point of all the metal plates joined by the weld metal, a first plating thickness reduction portion is provided in the zinc-plated layer inside the weld at the mating surface, the thickness of the zinc-plated layer in the first plating thickness reduction portion is 1.0 μm or more and 30.0 μm or less, and the first plating thickness reduction portion surrounds the weld metal at the mating surface.

Description

Technical Field

[0001] The present disclosure relates to a welded joint, a machine structural member, an automotive member, and a method for manufacturing a welded joint.

Background Art

[0002] A welded joint obtained by welding overlapping metal plates is used in various machine structural members such as automotive members. In addition, in order to enhance the corrosion resistance of a machine structural member, various corrosion-resistant coatings may be provided on the surface of the metal plate. An example of the corrosion-resistant coating is a zinc-based plating layer. Examples of welding methods for metal plates having a coating are disclosed in Patent Documents 1 to 5.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the melting point of the metal plate is higher than the boiling point of the zinc-based plating layer and the zinc-based plating layer is disposed on the mating surface of the overlapping metal plates, blowholes are likely to occur in the weld metal obtained by welding the metal plates. A blowhole is a cavity formed in the weld metal.

[0005] During welding, it is necessary to heat the metal plate to a temperature above its melting point to form a molten pool. At this time, the low-boiling-point zinc-based plating layer evaporates and penetrates the molten pool. When the molten pool solidifies, the vapor that has entered the molten pool forms blowholes. For example, if the metal plate is steel, blowholes are likely to occur in the weld metal.

[0006] One method for suppressing blowholes caused by vapor in the zinc-based plating layer is to create a gap between the overlapping surfaces of the metal plates. By allowing the vapor from the zinc-based plating layer to escape to the outside of the molten metal through this gap, blowholes can be suppressed.

[0007] However, gaps in the mating surfaces can compromise the stability of the welding process. In particular, in laser welding with small molten pool sizes, gaps in the mating surfaces are prone to causing welding defects such as burn-through. Furthermore, controlling the size of these gaps requires advanced production techniques. Therefore, suppressing blowholes using gaps in the mating surfaces complicates the manufacturing process of welded joints.

[0008] Another example of a method to suppress blowholes caused by vapor in the zinc-plated layer is to remove the zinc-plated layer from the area to be welded before welding. This reduces the amount of vapor and suppresses the occurrence of blowholes. However, removing the zinc-plated layer and forming an exposed base metal area impairs the corrosion resistance of the zinc-plated metal sheet. Reducing the width of the exposed base metal area is difficult because it is difficult to predict and precisely control the width of the weld metal at the mating surface.

[0009] In view of the above circumstances, the object of this disclosure is to provide a welded joint, a mechanical structural member, an automobile member, and a method for manufacturing a welded joint that can be easily manufactured, ensure the corrosion resistance of metal plates at the mating surface, and suppress blowholes in the weld metal. [Means for solving the problem]

[0010] The gist of this disclosure is as follows:

[0011] (1) A welded joint according to one aspect of the present disclosure comprises a weld having two or more stacked metal plates and a weld metal that joins the metal plates, wherein one or more of the metal plates are zinc-plated metal plates having a zinc-plated layer on one or both of their surfaces, the one or more zinc-plated layers are arranged on the mating surfaces of the metal plates, the boiling point of the zinc-plated layer arranged on the mating surfaces is lower than the melting point of all the metal plates joined by the weld metal, a first plating thickness reduction portion is provided in the zinc-plated layer inside the weld at the mating surfaces, the thickness of the zinc-plated layer in the first plating thickness reduction portion is 1.0 μm or more and 30.0 μm or less, and the first plating thickness reduction portion surrounds the weld metal at the mating surfaces. (2) Preferably, in the welded joint described in (1) above, the first plated thickness reduction portion is in contact with the weld metal at the mating surface. (3) Preferably, in the welded joint described in (2) above, the thickness of the zinc-based plating layer in the first plating thickness reduction portion that is in contact with the weld metal is 1.0 μm or more and 4.5 μm or less. (4) Preferably, in the welded joint described in any one of the above items (1) to (3), the zinc-plated metal sheet has a second plated thickness reduction portion between the first plated thickness reduction portion and the weld metal at the mating surface, and the thickness of the zinc-plated layer in the second plated thickness reduction portion is less than 1.0 μm. (5) Preferably, in the welded joint described in any one of the above items (1) to (4), the distance W1 between the edge of the first plated thickness reduction portion opposite to the weld metal and the weld metal is 0.35 mm or more and 5.00 mm or less. (6) Preferably, in the welded joint described in (4) or (5) above, the distance W2 between the edge of the second plating thickness reduction portion opposite to the weld metal and the weld metal is greater than 0 mm and less than or equal to 1.2 mm. (7) Preferably, in the welded joint described in any one of the above items (4) to (6), the difference between the distance W1 between the edge opposite to the weld metal of the first plated thickness reduction portion and the weld metal, and the distance W2 between the edge opposite to the weld metal of the second plated thickness reduction portion and the weld metal, is greater than 0 mm and less than or equal to 3.8 mm. (8) Preferably, in the welded joint described in any one of the above items (1) to (7), two or more of the metal plates are zinc-plated metal plates, the zinc-plated layers of each of the two zinc-plated metal plates are superimposed on the joint surface of the two zinc-plated metal plates, and each of the two zinc-plated metal plates has the first plating thickness reduction portion on the joint surface. (9) Preferably, in the welded joint described in any one of the above items (1) to (8), the zinc-based plating layer is a ternary plating layer containing Al and Mg, with the remainder being Zn and impurities. (10) Preferably, in the welded joint described in any one of the above items (1) to (9), the thickness of one or more of the metal plates is 0.5 mm or more and 3.0 mm or less. (11) Preferably, in the welded joint described in any one of the above items (1) to (10), the Vickers hardness of the metal plate is 150 HV or more and 750 HV or less.

[0012] (12) A mechanical structural member according to another aspect of the present disclosure comprises a welded joint as described in any one of paragraphs (1) to (11) above.

[0013] (13) Automotive components relating to another aspect of the present disclosure include a welded joint as described in any one of paragraphs (1) to (11) above.

[0014] (14) A method for manufacturing a welded joint according to another aspect of the present disclosure includes a step of forming a first plating thickness reduction portion on a zinc-based plated metal plate having a zinc-based plating layer on one or both surfaces, a step of stacking a plurality of metal plates including the zinc-based plated metal plate, and a step of welding the metal plates. When forming the first plating thickness reduction portion, the thickness of the zinc-based plating layer in the first plating thickness reduction portion is set to be 1.0 μm or more and 30.0 μm or less. When stacking the metal plates, at least one zinc-based plating layer and the first plating thickness reduction portion are arranged on the mating surface. When welding the metal plates, on the mating surface, a molten pool is formed inside the outer edge of the first plating thickness reduction portion, and the first plating thickness reduction portion around the outer edge is left in the welded portion. (15) Preferably, in the method for manufacturing a welded joint described in (14) above, when forming the first plating thickness reduction portion, a second plating thickness reduction portion is formed inside the first plating thickness reduction portion. When welding the metal plates, on the mating surface, the molten pool is formed in the second plating thickness reduction portion. (16) Preferably, in the method for manufacturing a welded joint described in (14) or (15) above, when welding the metal plates, on the mating surface, the molten pool is formed so as to cover the entire second plating thickness reduction portion and extend to the first plating thickness reduction portion. (17) Preferably, in the method for manufacturing a welded joint described in any one of (14) to (16) above, the first plating thickness reduction portion is formed by irradiation with a pulsed laser or machining, and the metal plates are welded using a continuous wave laser.

Effects of the Invention

[0015] The present disclosure can provide a welded joint, a mechanical structure member, an automotive member, and a method for manufacturing a welded joint that can be easily manufactured, ensure the corrosion resistance of the metal plates on the mating surface, and suppress blowholes in the welded metal.

Brief Description of the Drawings

[0016] [Figure 1]It is a perspective view of a hat-shaped member that is lap-welded. [Figure 2] It is a perspective view of a hat-shaped member that is lap fillet-welded. [Figure 3] It is a perspective view of a member where two pipes are joined. [Figure 4] It is a perspective view of a member where a round pipe and a flat plate are joined. [Figure 5] It is a schematic cross-sectional view of the lap joint shown in FIG. 1. [Figure 6] It is a schematic cross-sectional view of the lap joint shown in FIG. 2. [Figure 7] It is a schematic cross-sectional view of the lap joint shown in FIG. 3. [Figure 8] It is a schematic cross-sectional view of a welded part where the thickness of the zinc-based plating layer continuously changes around the weld metal. [Figure 9] It is a plan view of the mating surface of the lap joint in FIGS. 1 and 5. [Figure 10] It is a plan view of the mating surface of the lap fillet joint in FIGS. 2 and 6. [Figure 11] It is a schematic diagram of the process of forming a coating thickness reduction part on a zinc-based plated metal sheet. [Figure 12] It is a schematic diagram of the process of stacking a plurality of metal sheets. [Figure 13] It is a schematic diagram of the process of welding a plurality of metal sheets. [Figure 14A] It is a schematic cross-sectional view of Example A. [Figure 14B] It is a schematic cross-sectional view of Example B. [Figure 14C] It is a schematic cross-sectional view of Example C. [Figure 14D] It is a schematic cross-sectional view of Example D. [Figure 14E] It is a schematic cross-sectional view of Example E. [Figure 14F] It is a schematic cross-sectional view of Example F. [Figure 14G] It is a schematic cross-sectional view of Example G. [Figure 14H] It is a schematic cross-sectional view of Example H. [Figure 15A] It is a cross-sectional photograph of the weld metal of Example A. [Figure 15B] This is a cross-sectional photograph of the weld metal in Example B. [Figure 15C] This is a cross-sectional photograph of the weld metal in Example C. [Figure 15D] This is a cross-sectional photograph of the weld metal in Example D. [Figure 15E] This is a cross-sectional photograph of the weld metal in example E. [Figure 15F] This is a cross-sectional photograph of the weld metal in example F. [Figure 15G] This is a cross-sectional photograph of the weld metal in example G. [Figure 15H] This is a cross-sectional photograph of the weld metal in example H. [Figure 16] This is a schematic cross-sectional view of a welded joint example, created for reference, showing only the thicker second plating thickness reduction section. [Figure 17] Figure 16 is a cross-sectional photograph of the weld metal of the welded joint. [Modes for carrying out the invention]

[0017] (1. Welded joints) A welded joint 1 according to one aspect of the present disclosure comprises a welded portion 12 having two or more stacked metal plates 11 and a weld metal 121 that joins the metal plates 11. One or more metal plates 11 are zinc-plated metal plates 11C having a zinc-plated layer 111 on one or both surfaces. One or more zinc-plated layers 111 are arranged on the mating surface 13 of the metal plates 11. The boiling point of the zinc-plated layer 111 arranged on the mating surface 13 is lower than the melting point of all the metal plates 11 joined by the weld metal 121. At the mating surface 13, a first plating thickness reduction portion 1111 is provided in the zinc-plated layer 111 inside the welded portion 12. The thickness of the zinc-plated layer 111 in the first plating thickness reduction portion 1111 is 1.0 μm or more and 30.0 μm or less. At the mating surface 13, the first plating thickness reduction portion 1111 surrounds the weld metal 121. The details of the welded joint 1 will be described below with reference to Figure 1 and other figures as appropriate.

[0018] (Metal plate 11 and welded part 12) The welded joint 1 includes a weld 12. The term "welded joint" generally refers to the entire portion including the weld metal and the heat-affected zone. The term "heat-affected zone" generally refers to the unmelted portion of the base material that has undergone changes in structure, metallurgical properties, mechanical properties, etc., due to heat from welding, cutting, etc., and is also called HAZ (see JIS Z 3001-1:2018). In this disclosure, the weld 12 is defined as a region having two or more overlapping metal plates 11 and weld metal 121 joining these metal plates 11. Optionally, the weld 12 may have a heat-affected zone formed around the weld metal 121. However, the welded joint 1 may be heat-treated after welding. In this case, there is no heat-affected zone in the welded joint 1.

[0019] The term "metal plate" is a concept that includes not only members that are flat throughout, but also plate-like parts of mechanical structural members that have complex shapes. For example, the flange of a hat-shaped member and a pipe-shaped member formed by shaping a metal plate 11 into a cylindrical form are also considered to be a type of metal plate 11. The material of the metal plate 11 can be appropriately selected by a person skilled in the art depending on the application of the welded joint 1. Preferred examples of metal plates 11 are aluminum plates, titanium plates, and steel plates. In this disclosure, the number of metal plates means the number of plates overlapping in the weld. The term "two or more metal plates" means that the number of metal plates overlapping in the weld 12 is two or more. The number of metal plates in the welded joint 1 does not need to be two or more. For example, if the welded joint 1 is a pipe with a joint formed by rolling a metal plate and welding the ends, the number of metal plates 11 in the weld 12 is two, but the number of metal plates in the welded joint 1 is one. The number of metal plates 11 in the welded joint 1 may be one.

[0020] Examples of various welded joints 1 comprising the aforementioned metal plate 11 and welded joint 12 are shown in Figures 1 to 4. The terms "lap joint," "fillet joint," and "flare joint" are defined in JIS Z 3001-1:2018.

[0021] Figure 1 is a perspective view of a metal hat-shaped member. The flange of the hat-shaped member in Figure 1 is superimposed on a metal plate. The flange and the plate are spaced apart from the end of the flange and joined by weld metal 121 that penetrates the flange. The welded joint 1 in Figure 1 is a so-called lap joint.

[0022] Figure 2 is also a perspective view of a metal hat-shaped member. The flange of the hat-shaped member in Figure 1 is superimposed on a metal plate. The flange and the plate are joined by a weld metal 121. The weld metal 121 is provided at the end of the flange. The weld metal 121 joins the end of the flange to the surface of the plate. The weld metal 121 in Figure 2 is a fillet weld, and the welded joint 1 in Figure 2 is a so-called lap fillet joint.

[0023] Figure 3 is a perspective view of a member formed by joining two metal pipes having the same cross-sectional shape. The cross-section of the pipes is a rectangular shape with rounded vertices. The sides of the two pipes have four flat sections extending along the longitudinal direction of the pipes and four curved sections connecting these flat sections. The flat sections of the two pipes are overlapped. The overlapped flat sections correspond to the metal plate 11. The curved sections of the two pipes at both ends of the overlapped flat sections are joined by weld metal 121. The welded joint 1 in Figure 3 is a so-called flare joint. A flare joint is a joint having a groove-shaped section made of arcs, or a groove-shaped section made of arcs and straight lines.

[0024] Figure 4 is a perspective view of a component formed by joining a metal round pipe and a metal flat plate. The side of the round pipe and the surface of the flat plate are overlapped. The round pipe and the flat plate are joined by weld metal 121. The welded joint 1 in Figure 4 is also a flare joint.

[0025] The weld metal 121 exemplified in Figures 1 to 4 is all linear. However, the metal plate 11 may be spot-welded. For example, the weld metal 121 may be spot-shaped. An example of spot-shaped weld metal is a nugget produced by resistance spot welding. Also, the weld metal 121 exemplified in Figures 1 to 4 is all exposed on the surface of the welded joint 1. Such weld metal 121 is produced, for example, by laser welding or arc welding. However, the weld metal 121 may be formed only inside the welded joint 1. For example, a nugget formed by spot welding or seam welding is usually located only inside the welded joint 1 and is not exposed on the surface of the welded joint 1.

[0026] (Zinc-plated metal sheet 11C) One or more of the metal plates 11 in the welded joint 1 are zinc-plated metal plates 11C. A zinc-plated metal plate 11C is a metal plate 11 having a zinc-plated layer 111 on one or both of its surfaces. A zinc-plated layer is a plating layer mainly composed of Zn, optionally containing alloying elements such as Al, Mg, Si, and Fe. The zinc-plated layer 111 can improve the corrosion resistance of the metal plate 11. Specific examples of the zinc-plated layer 111 will be described later.

[0027] (Arrangement of zinc-based plating layer 111) At least one zinc-based plating layer 111 is placed on the mating surface 13 of the metal plates 11. The zinc-based plating layer 111 may also be placed in locations other than the mating surface 13. If there are three or more stacked metal plates 11 and two or more mating surfaces 13, the zinc-based plating layer 111 is placed on at least one of the mating surfaces 13. A welded joint in which the various configurations described later are filled on at least one mating surface 13 is considered to be a welded joint according to this embodiment.

[0028] The arrangement of the zinc-based plating layer 111 will be described below with reference to schematic cross-sectional diagrams such as Figure 5. For the sake of clarity, the zinc-based plating layer 111 is depicted as being very thick in the schematic cross-sectional diagrams of this disclosure. In reality, the thickness of the zinc-based plating layer on a zinc-based plated metal sheet 11C is very small compared to the thickness of the metal sheet 11. Also, the heat-affected zone is omitted in the schematic cross-sectional diagrams of this disclosure.

[0029] Figure 5 shows an example of a schematic cross-sectional view of the welded joint 12. Figure 5 shows a surface obtained by cutting the welded joint 12 of the lap joint shown in Figure 1 perpendicular to the weld line. In the welded joint 1 of Figure 5, the metal plate 11 on the upper side of the paper does not have a zinc-based plating layer 111. The metal plate 11 on the lower side of the paper is a zinc-plated metal plate 11C having a zinc-based plating layer 111 on one surface. The boundary between the metal plate 11 on the upper side of the paper and the zinc-based plating layer 111 is the mating surface 13. In the welded joint 1 of Figure 5, the two metal plates 11 are overlapped so that the zinc-based plating layer 111 is located on the mating surface 13.

[0030] Figure 6 shows another example of a schematic cross-sectional view of the welded joint 12. Figure 6 shows a surface obtained by cutting the welded joint 12 of the lap fillet joint shown in Figure 2 perpendicular to the weld line. In the welded joint 1 of Figure 6, the metal plate 11 on the upper side of the paper is a zinc-plated metal plate 11C having zinc-plated layers 111 on both of its surfaces. The metal plate 11 on the lower side of the paper is a zinc-plated metal plate 11C having a zinc-plated layer 111 on one of its surfaces. The interface between the two overlapping zinc-plated layers 111 is the mating surface 13. In the welded joint 1 of Figure 6, the two metal plates 11 are overlapped so that the zinc-plated layers 111 are positioned on the mating surface 13. Also, in the welded joint 1 of Figure 6, the two zinc-plated layers 111 are in contact at the mating surface 13.

[0031] Figure 7 shows another example of a schematic cross-sectional view of the welded joint 12. Figure 7 shows a surface obtained by cutting the welded joint 12 of the flare joint shown in Figure 3 perpendicular to the weld line. In the welded joint 1 of Figure 7, the metal plate 11 on the upper side of the paper is a zinc-plated metal plate 11C having a zinc-plated layer 111 on one surface. The metal plate 11 on the lower side of the paper is also a zinc-plated metal plate 11C having a zinc-plated layer 111 on one surface. The interface between the two overlapping zinc-plated layers 111 is the mating surface 13. In the welded joint 1 of Figure 7, the two metal plates 11 are overlapped so that the zinc-plated layers 111 are positioned on the mating surface 13. Also in the welded joint 1 of Figure 7, the two zinc-plated layers 111 are in contact at the mating surface 13.

[0032] (Boiling point of zinc-based plating layer 111) The boiling point of the zinc-based plating layer 111 on the mating surface 13 is lower than the melting point of all the metal plates 11 in the welded joint 1. The "boiling point of the zinc-based plating layer 111" refers to the temperature at which vapor begins to be generated from the zinc-based plating layer 111 when it is heated. The "melting point of the metal plate 11" refers to the temperature at which the metal plate 11 becomes completely liquid when it is heated. For example, the boiling point of pure zinc is approximately 900°C. If the zinc-based plating layer is made of pure zinc, the melting point of all the metal plates 11 in the welded joint 1 is above approximately 900°C. In order to manufacture a welded joint 1 made of such metal plates 11, the temperature of the weld area must be above 900°C.

[0033] When welding a metal plate 11 that has not undergone the removal of the zinc-based plating layer before welding, the zinc-based plating layer turns into vapor. This is because, when welding the metal plate 11, the temperature of the weld area 12 becomes higher than the melting point of the metal plate 11. The vapor generated at the joint surface 13 causes blowholes in the weld metal 121.

[0034] However, the zinc-based plating layer 111 disposed other than the mating surface 13 does not generate blowholes during welding. For example, the zinc-based plating layer 111 at the uppermost stage of the welding joint 1 illustrated in FIG. 6 is disposed outside the mating surface 13. The zinc-based plating layer 111 at the uppermost stage of the drawing in FIG. 6 becomes vapor during welding. However, the vapor of the zinc-based plating layer 111 at the uppermost stage of the drawing in FIG. 6 quickly scatters into the welding environment during welding and is not taken into the molten pool. Therefore, the vapor of the zinc-based plating layer 111 at the uppermost stage of the drawing in FIG. 6 does not cause blowholes. Also, the zinc-based plating layer 111 disposed on the right side of the welding metal 121 in the welding joint 1 illustrated in FIG. 6 is also outside the mating surface 13. The zinc-based plating layer 111 disposed in this portion also does not cause blowholes. When attempting to suppress blowholes, it is necessary to set the configuration of the zinc-based plating layer 111 disposed on the mating surface 13 to a predetermined one, but the zinc-based plating layer 111 disposed at other positions can be ignored.

[0035] (First plating thickness reduction portion 1111) In the mating surface 13, a first plating thickness reduction portion 1111 is provided in the zinc-based plating layer 111 inside the welded portion 12. The zinc plating layer in the first plating thickness reduction portion 1111 is thinner than the zinc-based plating layer outside the welded portion. Also, in the first plating thickness reduction portion 1111, the thickness of the zinc-based plating layer is set to be 1.0 μm or more and 30.0 μm or less. That is, the first plating thickness reduction portion is defined as a region where the thickness t2 of the zinc-based plating layer satisfies both of the following two equations. t2 < t1 Equation 1 1.0 ≤ t2 ≤ 30.0 Equation 2 t1 is the thickness of the zinc-based plating layer on the outside of the welded part, in units of μm. In the present disclosure, the thickness t1 of the zinc-based plating layer on the outside of the welded part is defined as the thickness of the zinc-based plating layer 111 measured outside the heat affected zone (HAZ). The position of the heat affected zone can be easily confirmed by corroding and observing the cross-section of the welded part using a reagent according to the material of the metal plate. The thickness of the zinc-based plating layer on the outside of the welded part can be measured by observing the cross-section of the zinc-based plating layer with SEM outside the heat affected zone. The SEM observation conditions can be the same as those for the SEM observation of the first plating thickness reduction part 1111 described later.

[0036] The shape and position of the first plating thickness reduction part 1111 are determined based on the thickness of the zinc-based plating layer 111. For example, as illustrated in FIG. 8, when the thickness of the zinc-based plating layer continuously changes around the weld metal 121, only the region where t2 < t1 and 1.0 ≦ t2 ≦ 30.0 are satisfied is regarded as the first plating thickness reduction part 1111.

[0037] Preferably, the thickness of the zinc-based plating layer in the first plating thickness reduction part 1111 is 20.0 μm or less, 15.0 μm or less, 10.0 μm or less, 5.0 μm, or 4.5 μm or less. Preferably, the thickness of the zinc-based plating layer in the first plating thickness reduction part 1111 is 1.1 μm or more, 1.5 μm or more, or 2.0 μm or more.

[0038] When changing the upper and lower limit values of the first plating thickness reduction part to the above-mentioned preferable values, Equation 2 described above is appropriately rewritten. For example, when the thickness of the zinc-based plating layer in the first plating thickness reduction part 1111 is defined as P μm or more and Q μm or less, the first plating thickness reduction part 1111 is defined as the region where the thickness t2 of the zinc-based plating layer satisfies both of the following two equations. t2 < t1 Equation 1 P ≦ t2 ≦ Q Equation 2A

[0039] At the mating surface 13, the first plating thickness reduction portion 1111 surrounds the weld metal 121. On the other hand, the zinc-based plating layer 111 outside the mating surface 13 does not necessarily need to have the first plating thickness reduction portion 1111. The arrangement of the first plating thickness reduction portion 1111 will be described in detail with reference to Figures 9 and 10, etc.

[0040] Figure 9 shows a plan view of the mating surface 13 of the lap joints in Figures 1 and 5. In Figure 9, the upper metal plate 11 in Figure 1 has been removed. In Figures 5 and 9, both the left and right sides of the weld metal 121 are included in the mating surface 13. Therefore, in Figures 5 and 9, the first plating thickness reduction portion 1111 surrounds both the right and left sides of the weld metal 121.

[0041] Figure 10 shows a plan view of the mating surface 13 of the lap fillet joints in Figures 2 and 6. In Figure 10, the upper metal plate 11 in Figures 2 and 6 has been removed. The dashed line X in Figure 10 indicates the edge of the upper metal plate 11 in Figures 2 and 6. In Figure 10, only the left side of the dashed line X is the mating surface 13. In Figures 2 and 10, only the left side of the plane of the weld metal 121 is included in the mating surface 13. Therefore, in Figures 2 and 10, the first plating thickness reduction portion 1111 surrounds only the left side of the weld metal 121. The right side of the dashed line X is outside the mating surface 13, and the first plating thickness reduction portion 1111 does not need to be provided there.

[0042] The configuration of the mating surface 13 of the flare joint in Figures 3 and 4 can be the same as in Figure 10. Between the pair of weld metals 121 in Figure 3, there is a mating surface 13 of the metal plate 11. A first plating thickness reduction portion 1111 needs to be provided here. On the other hand, the right and left sides of the weld metal 121 in Figure 3 are not mating surfaces 13 of the metal plate 11. A first plating thickness reduction portion 1111 does not need to be provided here. On the left side of the plane of the weld metal 121 in Figure 4, there is a mating surface 13 of the metal plate 11. A first plating thickness reduction portion 1111 needs to be provided here. On the other hand, the right side of the plane of the plane of the weld metal 121 in Figure 4 is not a mating surface 13 of the metal plate 11. A first plating thickness reduction portion 1111 does not need to be provided here.

[0043] The first plating thickness reduction portion 1111 surrounding the weld metal 121 may be in contact with the weld metal 121 or may be separated from the weld metal 121. In the welded joint 1 illustrated in Figures 5 and 6, the first plating thickness reduction portion 1111 is in contact with the weld metal 121. On the other hand, in the welded joint 1 illustrated in Figure 7, the first plating thickness reduction portion 1111 provided on the zinc-based plating layer 111 on the upper side of the paper is not in contact with the weld metal 121. In the welded joint 1 illustrated in Figure 8, the first plating thickness reduction portion 1111 provided on the zinc-based plating layer 111 is also not in contact with the weld metal 121.

[0044] If the first plating thickness reduction area 1111 and the weld metal 121 are not in contact, a second plating thickness reduction area 112 is provided between them, which is a region in which the thickness of the zinc-based plating layer 111 is less than 1.0 μm. In the second plating thickness reduction area 112, the thickness of the zinc-based plating layer 111 may be 0 μm. That is, in the second plating thickness reduction area 112, the base metal of the plated metal plate may be exposed. "Base metal" refers to the material on which the zinc-based plating layer 111 is deposited or formed. In the welded joint 1 according to this embodiment, a configuration in which the second plating thickness reduction area 112 exists is also permitted.

[0045] In addition to a low-boiling-point zinc-based plating layer that vaporizes during welding, a high-boiling-point coating that does not vaporize during welding may also be provided on the mating surface 13. The high-boiling-point coating that does not vaporize during welding does not necessarily need to have the first plating thickness reduction portion 1111. Furthermore, there may be two zinc-based plating layers on the mating surface 13. In this case, as illustrated in Figure 6, it is sufficient that at least one of the zinc-based plating layers has the first plating thickness reduction portion 1111. Preferably, as illustrated in Figure 7, all zinc-based plating layers included in the mating surface 13 have thickness reduction portions.

[0046] The method for determining the presence or absence of the first plating thickness reduction area 1111 is cross-sectional observation. Figures 9 and 10 show, for the sake of explanation, the two metal plates 11 disassembled and the mating surface 13 viewed from above. However, in reality, it is difficult to disassemble the welded joint 1 as shown in Figures 9 and 10 and observe the first plating thickness reduction area 1111 by viewing the mating surface 13 from above. This is because if the weld metal 121 is cut and the two metal plates 11 are separated as shown in Figures 9 and 10, scratches will occur in the zinc-based plating layer 111 on the mating surface 13, making it impossible to determine the shape of the first plating thickness reduction area 1111 before separation. Furthermore, when viewing the mating surface 13 from above, the thickness of the zinc-based plating layer cannot be accurately determined. Therefore, the evaluation of whether or not the first plating thickness reduction area 1111 surrounds the weld metal 121 on the mating surface 13 is performed by cross-sectional observation of the welded joint 12.

[0047] If the weld metal 121 is formed in a linear shape, the weld portion 12 is cut perpendicular to the weld line. If the weld metal 121 is formed in a point shape, the weld portion 12 is cut along an arbitrary plane that passes approximately through the center of the weld metal 121 and is perpendicular to the mating surface 13. The cross-section is then observed using an SEM and the thickness of the zinc-based plating layer on the mating surface 13 is measured. This allows for the determination of whether or not a first plating thickness reduction portion 1111 is formed on the mating surface 13. The analytical conditions adopted by the inventors were as follows. • SEM: JEOL Ltd. JSM-IT300 • EDS detector: JED-2300(SDD) • Acceleration voltage: 15kV ·Current: 78(PC)

[0048] When manufacturing the welded joint 1 according to this embodiment, a first plating thickness reduction portion 1111 is provided on the zinc-plated metal sheet 11C before welding the zinc-plated metal sheet 11C. Then, the weld metal 121 is formed in the first plating thickness reduction portion 1111. This makes it possible to form the first plating thickness reduction portion 1111 surrounding the weld metal 121. Details of the manufacturing method of the welded joint 1 will be described later.

[0049] (Effects and Benefits) The welded joint 1 according to this embodiment has a zinc-based plating layer 111 on its mating surface 13. The zinc-based plating layer 111 enhances the corrosion resistance of the mating surface 13, but may cause blowholes in the weld metal 121.

[0050] Therefore, the welded joint 1 according to this embodiment is provided with a first plating thickness reduction portion 1111 surrounding the weld metal 121. In the first plating thickness reduction portion 1111, the amount of zinc-based plating layer 111 is small. When the first plating thickness reduction portion 1111 is welded, the amount of vapor caused by the zinc-based plating layer 111 is small. Consequently, when the first plating thickness reduction portion 1111 is welded to form the weld metal 121, the occurrence of blowholes can be suppressed.

[0051] Furthermore, in the first plated thickness reduction section 1111, the base metal of the zinc-plated metal sheet 11C is not exposed. Therefore, the corrosion resistance in the first plated thickness reduction section 1111 is higher than that in the second plated thickness reduction section 112. The first plated thickness reduction section 1111 ensures the corrosion resistance of the metal sheet 11 at the mating surface 13 of the welded joint 1.

[0052] In addition, the welded joint 1 according to this embodiment does not require a configuration for releasing steam generated at the mating surface 13 to the outside. In the prior art, blowholes are suppressed by providing a gap in the mating surface 13 and releasing steam from the welded part 12 to the outside through the gap. However, advanced production technology is required to control the size of the gap in the mating surface 13. On the other hand, the welded joint 1 according to this embodiment can be manufactured without providing a gap in the mating surface 13. Therefore, the welded joint 1 according to this embodiment can be easily manufactured.

[0053] The most basic embodiment of the welded joint 1 according to this embodiment has been described above. A more preferred embodiment will be described below.

[0054] (A configuration in which the second plating thickness reduction portion 112 is not provided) As described above, the first plating thickness reduction portion 1111 surrounding the weld metal 121 may be in contact with the weld metal 121. In the welded joint 1 illustrated in Figures 5 and 6, the first plating thickness reduction portion 1111 is in contact with the weld metal 121. Also, in the zinc-plated metal plate 11C on the lower side of the welded joint 1 illustrated in Figure 7, the first plating thickness reduction portion 1111 is in contact with the weld metal 121.

[0055] In the first plated thickness reduction portion 1111 that is in contact with the weld metal 121, the thickness of the zinc-based plating layer is preferably 1.0 μm or more and 4.5 μm or less. This further reliably suppresses blowholes.

[0056] (A configuration in which a second plating thickness reduction portion 112 is provided) On the other hand, the zinc-plated metal sheet 11C may have a second plating thickness reduction portion 112 between the first plating thickness reduction portion 1111 and the weld metal 121 at the mating surface 13. The second plating thickness reduction portion 112 is defined as the region in which the thickness t3 of the zinc-plated layer satisfies the following formula. t3<1.0 Equation 3 In the second plating thickness reduction area 112, the thickness t3 of the zinc-based plating layer is less than 1.0 μm. The second plating thickness reduction area 112 may also include a region where the thickness of the zinc-based plating layer is 0 μm, i.e., a region where the base metal of the zinc-plated metal sheet 11C is exposed.

[0057] The second plating thickness reduction portion 112 is in contact with the weld metal 121. In the zinc-plated metal plate 11C on the upper side of the welded joint 1 illustrated in Figure 7, the first plating thickness reduction portion 1111 is not in contact with the weld metal 121, and the second plating thickness reduction portion 112 is provided between the first plating thickness reduction portion 1111 and the weld metal 121.

[0058] In the second plating thickness reduction section 112, the corrosion resistance improvement effect of the zinc-based plating layer is weak. Therefore, the second plating thickness reduction section 112 is not very desirable from the viewpoint of improving the corrosion resistance of the mating surface 13. On the other hand, by providing the second plating thickness reduction section 112 on the zinc-based plated metal sheet 11C as illustrated in Figure 11 before welding the metal sheet 11, the blowhole suppression effect can be further enhanced.

[0059] Preferably, the second plating thickness reduction portion 112 of the zinc-plated metal sheet 11C before welding is incorporated into the weld metal 121 and disappears during welding. In this case, the first plating thickness reduction portion 1111 surrounding the weld metal 121 is in contact with the weld metal 121. However, the second plating thickness reduction portion 112 may remain after welding. In the welded joint 1 according to this embodiment, the corrosion resistance of the mating surface 13 is enhanced by the first plating thickness reduction portion 1111, so the remaining second plating thickness reduction portion 112 is acceptable.

[0060] (Width of the first plating thickness reduction section 1111, and width of the second plating thickness reduction section 112) In this disclosure, the edge of the first plating thickness reduction portion 1111 opposite to the weld metal 121 is referred to as the outer edge 1111E of the first plating thickness reduction portion. The distance W1 between the outer edge of the first plating thickness reduction portion and the weld metal is indicated by the symbol W1 in Figure 5, etc. In a welded joint 1 without a second plating thickness reduction portion 112, W1 is the width of the first plating thickness reduction portion 1111. In a welded joint 1 with a second plating thickness reduction portion 112, W1 is the sum of the widths of the first plating thickness reduction portion 1111 and the second plating thickness reduction portion 112.

[0061] Furthermore, in this disclosure, the edge of the second plating thickness reduction portion 112 opposite to the weld metal 121 is referred to as the outer edge 112E of the second plating thickness reduction portion. The distance W2 between the outer edge of the second plating thickness reduction portion and the weld metal is indicated by the symbol W2 in Figure 5, etc. W2 is the width of the second plating thickness reduction portion 112. Also, in the welded joint 1 having the second plating thickness reduction portion 112, W1-W2 is the width of the first plating thickness reduction portion 1111. Both W1 and W2 are determined by cross-sectional observation of the weld 12.

[0062] The wider the first plating thickness reduction section 1111 and the wider the second plating thickness reduction section 112, the lower the control accuracy required for welding the welding width during welding the metal plate 11 can be. This makes the manufacturing of the welded joint 1 even easier. On the other hand, the narrower the width of the second plating thickness reduction section 112, the higher the corrosion resistance of the mating surface 13 can be. Also, the narrower the width of the first plating thickness reduction section 1111 and the narrower the second plating thickness reduction section 112, the shorter the time required to form the first plating thickness reduction section 1111 and the second plating thickness reduction section 112.

[0063] Considering the above circumstances, preferably, the gap W1 between the edge opposite the weld metal 121 of the first plating thickness reduction portion 1111 and the weld metal is 0.35 mm or more and 5.00 mm or less. More preferably, W1 is 0.40 mm or more, 0.50 mm or more, or 1.00 mm or more. Even more preferably, W1 is 4.00 mm or less, 3.50 mm or less, or 3.00 mm or less.

[0064] When the welded joint 1 includes a second plated thickness reduction portion 112, preferably the gap W2 between the edge of the second plated thickness reduction portion 112 opposite to the weld metal 121 and the weld metal is greater than 0 mm and 1.2 mm or less. More preferably, W2 is 0.1 mm or more, 0.2 mm or more, or 0.4 mm or more. Even more preferably, W2 is 1.0 mm or less, 0.8 mm or less, or 0.6 mm or less.

[0065] When the welded joint 1 includes a second plated thickness reduction portion 112, preferably the difference between the gap W1 between the opposite edge of the weld metal 121 of the first plated thickness reduction portion 1111 and the weld metal, and the gap W2 between the opposite edge of the weld metal 121 of the second plated thickness reduction portion 112 and the weld metal, is greater than 0 mm and less than or equal to 3.8 mm. More preferably, W1-W2 is 0.1 mm or more, 0.2 mm or more, or 0.5 mm or more. Even more preferably, W1-W2 is 3.0 mm or less, 2.5 mm or less, or 2.0 mm or less.

[0066] Furthermore, as illustrated in Figure 5, when both sides of the weld metal 121 are mating surfaces 13, the above-mentioned provisions regarding the width of the first plating thickness reduction portion 1111 and the second plating thickness reduction portion 112 are preferably satisfied on at least one side of the weld metal 121, and more preferably on both sides of the weld metal 121. As illustrated in Figures 6 and 7, when two low-melting-point zinc-based plating layers 111 are arranged on the mating surface 13, the above-mentioned provisions regarding the width of the first plating thickness reduction portion 1111 and the second plating thickness reduction portion 112 are preferably satisfied on at least one of the zinc-based plating layers 111, and more preferably on both of the zinc-based plating layers 111.

[0067] (Overlapping two zinc-plated metal plates 11C) As illustrated in Figures 6 and 7, two or more of the multiple metal plates 11 included in the welded joint 1 are zinc-plated metal plates 11C having a zinc-plated layer 111, and the zinc-plated layers 111 of the two zinc-plated metal plates 11C may be overlapped at the mating surface 13 of the two zinc-plated metal plates 11C. In this case, as illustrated in Figure 6, only one of the zinc-plated metal plates 11C may have a first plating thickness reduction portion 1111 at the mating surface 13. On the other hand, as illustrated in Figure 7, each of the two zinc-plated metal plates 11C may have a first plating thickness reduction portion 1111 at the mating surface 13. When the first plating thickness reduction portion 1111 is provided on only one of the zinc-plated layers 111, the corrosion resistance of the mating surface 13 is further improved, and the time required to form the first plating thickness reduction portion 1111 is shortened. When the first plating thickness reduction portion 1111 is provided on both zinc-plated layers 111, blowholes are further suppressed.

[0068] (Aspect of the zinc-based plating layer 111) Preferably, the zinc-based plating layer 111 is a ternary plating layer containing Al and Mg, with the remainder being Zn and impurities. Suitable examples of the zinc-based plating layer 111 are GA plating layers, GI plating layers, EG plating layers, ternary Zn plating layers, Galtite layers, Galvanium layers, and Zn-Ni plating layers. Examples of ternary Zn plating layers are ZAM®, SuperDyma®, and ZEXEED®. The zinc-based plated metal sheet 11C may also contain an alloy layer of the plating layer and the steel sheet, formed by alloying the steel sheet having these plating layers. The thickness of the zinc-based plating layer 111 on the outside of the weld is preferably, for example, 15 to 100 μm.

[0069] (Appearance of the metal plate 11) Preferably, the thickness of one or more metal plates 11 is 0.5 mm or more and 3.0 mm or less. This makes it easy to apply the welded joint 1 according to this embodiment to an automobile component. More preferably, the thickness of the metal plate 11 is 0.8 mm or more, 1.0 mm or more, or 1.2 mm or more. More preferably, the thickness of the metal plate 11 is 2.8 mm or less, 2.5 mm or less, or 2.0 mm or less. Note that the term "thickness of the metal plate 11" means the thickness including the zinc-based plating layer 111 if a zinc-based plating layer 111 is provided on the surface of the metal plate 11.

[0070] Preferably, the Vickers hardness of the metal plate 11 is 150 HV or more and 750 HV or less. This makes it easy to apply the welded joint 1 according to this embodiment to an automobile component. More preferably, the Vickers hardness of the metal plate 11 is 180 HV or more, 200 HV or more, or 300 HV or more. More preferably, the hardness of the metal plate 11 is 700 HV or less, 680 HV or less, or 650 HV or less. Note that the term "hardness of the metal plate 11" refers to the hardness of the base metal when a zinc-based plating layer 111 is provided on the surface of the metal plate 11.

[0071] (2. Mechanical structural components) A mechanical structural member according to another aspect of this disclosure comprises a welded joint 1 according to this embodiment. This makes the mechanical structural member according to this embodiment easily manufacturable, ensures corrosion resistance of the metal plate 11 at the mating surface 13, and suppresses blowholes in the weld metal 121. A preferred example of the mechanical structural member is an automotive component, which will be described later. Furthermore, the mechanical structural member according to this embodiment can also be applied to building components and the like.

[0072] (3. Automotive components) An automotive component according to another aspect of the present disclosure comprises a welded joint 1 according to this embodiment. This makes the automotive component according to this embodiment easily manufacturable, ensures corrosion resistance of the metal plate 11 at the mating surface 13, and suppresses blowholes in the weld metal 121.

[0073] A preferred example of an automotive component is a structural component of an automobile body. Examples of structural components of an automobile body include bumpers, roof rails, pillars, side sills, and side members, as well as components to which reinforcements and subframes are joined. Suspension components such as arms and their reinforcements, as well as seat rails, can also be automotive components according to this embodiment. Battery storage components such as battery packs and battery modules, and their reinforcements, can also be automotive components according to this embodiment.

[0074] (4. Method for manufacturing welded joint 1) A method for manufacturing a welded joint 1 according to one aspect of the present disclosure comprises the steps of: forming a first plating thickness reduction portion 1111 on a zinc-plated metal sheet 11C having a zinc-plated layer 111 on one or both surfaces; stacking a plurality of metal sheets 11 including the zinc-plated metal sheet 11C; and welding the metal sheets 11. When forming the first plating thickness reduction portion 1111, the thickness of the zinc-plated layer 111 in the first plating thickness reduction portion 1111 is set to 1.0 μm or more and 30.0 μm or less. When stacking the metal sheets 11, at least one zinc-plated layer 111 and the first plating thickness reduction portion 1111 are placed on the mating surface 13. When welding the metal sheets 11, a molten pool 200 is formed inside the outer edge 1111E of the first plating thickness reduction portion 1111 on the mating surface 13, and the first plating thickness reduction portion 1111 around the outer edge 1111E is left in the welded portion 12.

[0075] According to the manufacturing method of the welded joint 1 of this embodiment, the above-described welded joint 1 can be suitably manufactured. Preferred embodiments of the above-described welded joint 1 can be appropriately added to the manufacturing method of the welded joint 1 shown below. However, the manufacturing method described below does not limit the scope of the welded joint 1 of this embodiment. The details of the manufacturing method of the welded joint 1 are described below.

[0076] (S1 Formation of the first plated thickness reduction portion 1111) First, as illustrated in Figure 11, a first plating thickness reduction section 1111 is formed on the zinc-plated metal sheet 11C. At this time, the thickness of the zinc-plated layer in the first plating thickness reduction section 1111 is set to 1.0 μm or more and 30.0 μm or less.

[0077] The location where the first plating thickness reduction portion 1111 is formed is the location where welding is planned. For example, if the weld metal 121 is a linear weld bead as illustrated in Figure 1, the first plating thickness reduction portion 1111 is formed in a strip shape as illustrated in Figure 11. If the weld metal 121 is a point-shaped weld metal 121 such as a nugget of a spot weld, the first plating thickness reduction portion 1111 can also be formed in a point shape.

[0078] Preferably, as illustrated in Figure 11, a second plating thickness reduction portion 112 is formed when the first plating thickness reduction portion 1111 is formed. In the second plating thickness reduction portion 112, the base metal of the zinc-plated metal sheet 11C is exposed. The position where the second plating thickness reduction portion 112 is formed is also a position where welding is planned. Furthermore, the second plating thickness reduction portion 112 is formed inside the first plating thickness reduction portion 1111.

[0079] As illustrated in Figures 1 and 5, when both sides of the weld metal 121 of the manufactured welded joint 1 are included in the mating surface 13, the second plating thickness reduction portion 112 is provided in the center of the first plating thickness reduction portion 1111, as illustrated in Figure 11. That is, the first plating thickness reduction portions 1111 are provided on both sides of the second plating thickness reduction portion 112. On the other hand, as illustrated in Figures 2, 3, 6, and 7, when only one side of the weld metal 121 of the manufactured welded joint 1 is included in the mating surface 13, it is sufficient to provide the first plating thickness reduction portion 1111 only on one side of the second plating thickness reduction portion 112.

[0080] In the zinc-plated metal sheet 11C before welding, the outer edge of the first plating thickness reduction portion 1111 coincides with the outer edge 1111E of the first plating thickness reduction portion in the welded joint 1. Furthermore, when the metal sheet 11 is welded while leaving the second plating thickness reduction portion 112, the outer edge of the second plating thickness reduction portion 112 coincides with the outer edge 112E of the second plating thickness reduction portion in the welded joint 1. In this disclosure, the boundary between the first plating thickness reduction portion 1111 in the zinc-plated metal sheet 11C before welding and the area outside it where the zinc-plated layer removal treatment has not been performed is also referred to as the outer edge 1111E of the first plating thickness reduction portion. Furthermore, the boundary between the first plating thickness reduction portion 1111 and the second plating thickness reduction portion 112 in the zinc-plated metal sheet 11C before welding is also referred to as the outer edge 112E of the second plating thickness reduction portion.

[0081] The distance between the outer edge 1111E of the first plating thickness reduction portion and the outer edge 112E of the second plating thickness reduction portion in the zinc-plated metal sheet before welding, i.e., the width W3 of the first plating thickness reduction portion, is not limited. From the viewpoint of further reducing the vapor of the zinc-plated layer 111 and further suppressing blowholes, a smaller width W3 of the first plating thickness reduction portion is preferable. On the other hand, from the viewpoint of improving the corrosion resistance of the mating surface 13, a larger width W3 of the first plating thickness reduction portion is preferable. When the metal sheet 11 is welded so as to leave the second plating thickness reduction portion 112, the width W3 of the first plating thickness reduction portion in the zinc-plated metal sheet before welding will be approximately the same as the widths W1-W2 of the first plating thickness reduction portion 1111 of the welded joint 1 described above. The preferred numerical range of W1-W2 described above may be applied to the width W3 of the first plating thickness reduction portion in the zinc-plated metal sheet before welding.

[0082] The means for forming the first plating thickness reduction portion 1111 and the second plating thickness reduction portion 112 are not particularly limited. Those skilled in the art can select an appropriate means depending on the material of the zinc-based plating layer 111. For example, the first plating thickness reduction portion 1111 and the second plating thickness reduction portion 112 can be formed by irradiation with a pulsed laser. Alternatively, the first plating thickness reduction portion 1111 and the second plating thickness reduction portion 112 can also be formed by cutting.

[0083] The pulsed laser used to form the first and second plating thickness reduction zones can be, for example, a nanosecond pulsed laser, a femtosecond pulsed laser, a picosecond pulsed laser, or a microsecond pulsed laser. These plating thickness reduction zones can also be formed using a continuous laser.

[0084] Simultaneously with the irradiation of the laser beam, an assisting gas such as air or an inert gas may be blown onto the processing area irradiated by the laser beam. Examples of inert gases include nitrogen or argon. The assisting gas plays a role in removing the plating that has melted or evaporated due to the laser irradiation. By blowing the assisting gas, the laser beam reaches the metal plate without being obstructed by the melted or evaporated plating. Therefore, the plating removal proceeds stably with the help of the assisting gas.

[0085] (S2 Overlapping of metal plates 11) Next, as illustrated in Figure 12, a plurality of metal plates 11, including a zinc-plated metal plate 11C, are stacked on top of each other. The plurality of metal plates 11 are the base materials of the welded joint 1. When stacking the metal plates 11, at least one zinc-plated layer 111 and a first plating thickness reduction portion 1111 provided on the zinc-plated layer 111 are placed on the mating surface 13.

[0086] (S3 Welding of metal plate 11) Then, as illustrated in Figure 13, multiple metal plates 11, including a zinc-plated metal plate 11C, are welded together. The welding method is not particularly limited. For example, it is preferable to weld the multiple metal plates 11 by laser welding using a laser beam 100. The arrows shown in Figure 13 indicate the direction of movement of the laser beam 100. In laser welding, it is preferable to use a continuous-wave laser. Alternatively, the multiple metal plates 11 may be welded by welding methods such as arc welding, spot welding, and seam welding.

[0087] The welding position is the region where the first plating thickness reduction section 1111 is provided. When welding the metal plate 11, a molten pool 200 is formed inside the outer edge 1111E of the first plating thickness reduction section at the joint surface 13. The molten pool 200 is a pool of molten metal created by heat during welding.

[0088] The area enclosed by the outer edge 1111E of the first plating thickness reduction is incorporated into the molten pool 200 and disappears. At this time, the first plating thickness reduction area 1111 may be incorporated into the molten pool 200 and turn into a small amount of vapor. However, since the amount of zinc-based plating layer 111 in the first plating thickness reduction area 1111 is small, the generation of blowholes due to vapor from the zinc-based plating layer 111 is suppressed.

[0089] Furthermore, when welding the metal plate 11, the first plated thickness reduction portion 1111 around the outer edge is left in the welded portion 12. For example, by making the size of the area surrounded by the outer edge 1111E of the first plated thickness reduction portion sufficiently larger than the expected size of the molten pool 200, the first plated thickness reduction portion 1111 can be left in the welded portion 12. After the molten pool 200 solidifies into weld metal 121, the first plated thickness reduction portion 1111 left in the welded portion 12 surrounds the weld metal 121. The first plated thickness reduction portion 1111 improves the corrosion resistance of the mating surface 13.

[0090] When a zinc-plated metal sheet 11C is provided with a second plating thickness reduction section 112, when welding the metal sheet 11, a molten pool 200 is formed in the second plating thickness reduction section 112 at the joint surface 13. The second plating thickness reduction section 112 does not generate steam when it is incorporated into the molten pool 200. Therefore, the second plating thickness reduction section 112 can further suppress the occurrence of blowholes in the zinc-plated layer 111 due to steam.

[0091] Unlike the first plated thickness reduction portion 1111, it is not necessary to leave the second plated thickness reduction portion 112 in the welded portion 12. From the viewpoint of improving the corrosion resistance of the mating surface 13, it is preferable to completely incorporate the second plated thickness reduction portion 112 into the weld metal 121. Therefore, when welding the metal plate 11, it is preferable to form the molten pool 200 at the mating surface 13 so as to cover the entire second plated thickness reduction portion 112 and extend to the first plated thickness reduction portion 1111. On the other hand, from the viewpoint of further suppressing blowholes, it is preferable to form the molten pool 200 inside the second plated thickness reduction portion 112 and leave the area around the outer edge 112E of the second plated thickness reduction portion untouched. This can further reduce the amount of steam generated. [Examples]

[0092] The effects of one aspect of this disclosure will be further illustrated by the examples. However, the conditions in the examples are merely examples of conditions adopted to confirm the feasibility and effectiveness of this disclosure. This disclosure is not limited to these examples of conditions. This disclosure may adopt various conditions as long as they do not depart from its gist and achieve its objectives.

[0093] Various welded joints were manufactured by overlapping and welding two zinc-plated metal sheets. The manufacturing conditions common to all welded joints were as follows:

[0094] • Type of zinc-plated metal sheet: GA980 (Alloyed hot-dip galvanized steel sheet with strength grade 980 MPa, as specified in JIS G 3302:2019 "Hot-dip galvanized steel sheets and strips") • Thickness of zinc-plated metal sheet: 1.6mm for both top and bottom plates. • Types of zinc-based plating layers: Zinc • Thickness of the zinc-based plating layer before the formation of the plated thickness reduction area: 10.4 μm Welding conditions: • Laser output: 7.5kW • Welding speed: 6m / min • Laser spot diameter: φ0.6mm Conditions for removing the entire plating layer thickness: • Average output power of pulsed laser: 2kW • Pulse width: 25ns • Pulse repetition rate: 300kHz • Laser scanning speed: 10 m / s • Number of repeated irradiations: 10 • Laser spot diameter: 0.68mm square • Scanline spacing: 0.60 mm • Conditions for removing partial thickness of the plated layer: • Average output power of pulsed laser: 2kW • Pulse width: 25ns • Pulse repetition rate: 300kHz • Laser scanning speed: 10 m / s • Number of repeated irradiations: 2 times, 4 times, 6 times • Laser spot diameter: 0.68mm square • Scanline spacing: 0.60 mm The terms "average power," "pulse width," and "pulse repetition rate" follow the definitions in JIS Z 3001-5:2013 "Welding Terminology - Part 5: Laser Welding." "Laser scan speed" refers to the movement speed of the laser irradiation unit. "Number of repeated irradiations" refers to the number of times the pulsed laser is repeatedly irradiated onto the same position.

[0095] When manufacturing some welded joints, a first plating thickness reduction section 1111 and a second plating thickness reduction section 112 were formed on the zinc-plated metal sheets before they were stacked. The shapes of the first plating thickness reduction section 1111 and the second plating thickness reduction section 112 were made identical on the two stacked zinc-plated metal sheets. Table 1 shows the structure of the zinc-plated metal sheets before welding. Figures 14A to 14H show schematic cross-sectional diagrams of the stacked zinc-plated metal sheets before welding. The dashed lines in these figures represent the fusion boundary FL. The fusion boundary FL is the boundary between the weld metal and the base metal.

[0096] The "width W4 of the second plating thickness reduction area" in Table 1 refers to the width W4 of the second plating thickness reduction area 112 in the zinc-plated metal sheet 11C before welding, as shown in Figures 14B to 14H. The "width W3 of the first plating thickness reduction area" in Table 1 refers to the width W3 of the first plating thickness reduction area 1111 in the zinc-plated metal sheet 11C before welding, as shown in Figures 14C to 14H.

[0097] As shown in Figures 14C to 14H, in the zinc-plated metal sheet before welding, first plating thickness reduction sections 1111 were provided on both sides of the second plating thickness reduction section 112. The width of both first plating thickness reduction sections 1111 was the same. Table 1 shows the width W3 of one of the first plating thickness reduction sections 1111. Also, W3 and W4 are not values ​​determined by cross-sectional observation, but rather the width of the laser-irradiated area. The thickness of the zinc-plated layer 111 was generally uniform in both the first plating thickness reduction section 1111 and the second plating thickness reduction section 112.

[0098] In some examples, the "width W4 of the second plating thickness reduction area" is stated as 0 mm. In such examples, the second plating thickness reduction area 112 was not formed on the zinc-plated metal sheet before welding. Also, in some examples, the "width W3 of the first plating thickness reduction area" is stated as 0 mm. In such examples, the first plating thickness reduction area 1111 was not formed on the zinc-plated metal sheet before welding.

[0099] In Table 1, "Plating thickness t2 of the first plating thickness reduction area before welding" refers to the thickness of the zinc-based plating layer 111 measured in the first plating thickness reduction area 1111 before welding. The thickness of the zinc-based plating layer 111 was measured in the cross-section of the first plating thickness reduction area. A plating thickness measurement area with a width of 50 μm was set in the center of the width direction of the first plating thickness reduction area 1111. The cross-sectional area of ​​the plating in this area was measured. The average value of the thickness of the zinc-based plating layer 111 in the plating thickness measurement area was calculated by dividing the cross-sectional area of ​​the plating by 50 μm. This average value is listed in the "Plating thickness t2 of the first plating thickness reduction area before welding" column of Table 1.

[0100] Furthermore, in all examples, the plating thickness of the second plating thickness reduction area 112 before welding was 0 μm, and the base metal was exposed there. Therefore, the plating thickness of the second plating thickness reduction area 112 was not listed in Table 1.

[0101] [Table 1]

[0102] Next, the cross-sections of welded joints obtained by welding various zinc-plated metal sheets listed in Table 1 were observed. The width of the first plating thickness reduction section 1111 and the plating thickness in the first plating thickness reduction section 1111 were measured. The observation results are shown in Table 2. Furthermore, cross-sectional photographs of the weld metal were taken. The photographs are shown in Figures 15A to 15H. Note that the plating thickness was measured in a cross-section perpendicular to the weld line, while the cross-sectional photographs of the weld metal were taken in a cross-section parallel to the weld line. Specifically, the cross-sectional photographs of the weld metal were taken in a cross-section parallel to the weld line, passing approximately through the center of the weld metal and perpendicular to the surface of the metal sheet.

[0103] In all examples of welded joints in Table 2, the second plating thickness reduction area 112 was absent, and its width was 0 mm. Therefore, the width of the second plating thickness reduction area 112 was not recorded in Table 2. Also, in all examples of welded joints in Table 2, the first plating thickness reduction area 1111 was in contact with the weld metal.

[0104] In Table 2, "W1L width of the left first plating thickness reduction section" refers to the width of the first plating thickness reduction section 1111 located on the left side of the weld metal. "W1R width of the right first plating thickness reduction section" refers to the width of the first plating thickness reduction section 1111 located on the right side of the weld metal. Figures 14C to 14H show the measurement locations of W1L and W1R. Although two zinc-based plating layers 111 were placed on the mating surface, the width of the upper first plating thickness reduction section 1111 and the width of the lower first plating thickness reduction section 1111 were approximately the same. Therefore, only the width of the upper first plating thickness reduction section 1111 is listed in Table 2.

[0105] The "plating thickness t2 of the first plating thickness reduction area after welding" is the value measured near the outer edge 1111E of the first plating thickness reduction area 1111 after welding. A plating thickness measurement area with a width of 50 μm was set near the outer edge 1111E of the first plating thickness reduction area 1111. The cross-sectional area of ​​the zinc-based plating layer 111 in this area was measured. The unit of measurement for the zinc-based plating layer 111 was then measured in μm. 2 The cross-sectional area was divided by 50 μm to calculate the average thickness of the zinc-based plating layer 111 in the plating thickness measurement area. This average value is listed in the "Plating thickness t2 of the first plating thickness reduction area after welding" column of Table 2. In Figures 15C to 15H, there are four outer edges 1111E of the first plating thickness reduction area 1111 (upper left, lower left, upper right, and lower right). In this experiment, the plating thickness measurement area was set near the lower right outer edge 1111E.

[0106] [Table 2]

[0107] As shown in Figure 15A, in Example A, where the first plating thickness reduction area 1111 and the second plating thickness reduction area 112 were not formed, significant blowholes occurred in the weld metal. As shown in Figure 15B, in Example B, where a narrow second plating thickness reduction area 112 was formed but the first plating thickness reduction area 1111 was not formed, significant blowholes also occurred in the weld metal.

[0108] On the other hand, as shown in Figures 15C to 15H, in Examples C to H, where a first plating thickness reduction section 1111 was formed in addition to the second plating thickness reduction section 112, the amount of blowholes generated in the weld metal was reduced compared to Examples A and B. In particular, in Examples E and H, where the thickness of the zinc-based plating layer 111 in the first plating thickness reduction section 1111 was 4.5 μm or less, almost no blowholes were generated.

[0109] Furthermore, for reference, a welded joint was created using a zinc-plated metal sheet in which only the thick second plating thickness reduction portion 512 was formed in the zinc-plated layer 511. A schematic cross-sectional view of this is shown in Figure 16, and a cross-sectional photograph of the weld metal is shown in Figure 17. In the welded joint in Figure 16, a wide second plating thickness reduction portion 512 was formed around the weld metal, while the first plating thickness reduction portion 1111 was absent. In the welded joint in Figure 16, almost no blowholes occurred in the weld metal. However, the corrosion resistance of the welded joint in Figure 16 is presumed to be inferior to that of the welded joints in Examples A to H.

[0110] In Examples E and H, the first plating thickness reduction section 1111, where a thin zinc-based plating layer 111 exists, was in contact with the weld metal. Therefore, it is highly likely that some vapor from the zinc-based plating layer was generated during the manufacturing process of Examples E and H. Nevertheless, Examples E and H were able to suppress the occurrence of blowholes to the same extent as the welded joint in Figure 16, which has a thicker second plating thickness reduction section 512.

[0111] In the weld metals of Examples C, D, F, and G, some blowholes were observed. However, by optimizing the width of the second plating thickness reduction section 112 before welding, it is considered possible to further suppress blowholes in the weld metals of these examples. [Explanation of Symbols]

[0112] 1. Welded joint 11 Metal plate 11C zinc-plated metal sheet 111 Zinc-based plating layer 1111 First plated thickness reduction area 1111E Outer edge of the first plated thickness reduction area 112 Second plated thickness reduction area 112E Outer edge of the second plated thickness reduction area 12 Welded parts 121 Weld metal 13 mating surface t1 Thickness of the zinc-based plating layer on the outside of the welded area t2 Thickness of the zinc-based plating layer in the first plated thickness reduction area W1 Distance between the outer edge of the first plated thickness reduction area and the weld metal W2 Distance between the outer edge of the second plated thickness reduction area and the weld metal W3 Width of the first plated thickness reduction area in the zinc-plated metal sheet before welding 100 laser beams 200 molten pools

Claims

1. The device comprises a welded section having two or more stacked metal plates and a weld metal that joins the metal plates, The one or more metal plates are zinc-plated metal plates having a zinc-plated layer on one or both of their surfaces. One or more of the zinc-based plating layers are arranged on the mating surfaces of the metal plates. The boiling point of the zinc-based plating layer disposed on the mating surface is lower than the melting point of all the metal plates joined by the weld metal. In the aforementioned mating surface, a first plated thickness reduction portion is provided in the zinc-based plating layer inside the welded portion. The thickness of the zinc-based plating layer in the first plated thickness reduction portion is 1.0 μm or more and 30.0 μm or less. In the aforementioned mating surface, the first plated thickness reduction portion surrounds the weld metal. Welded joint.

2. The welded joint according to claim 1, characterized in that the first plated thickness reduction portion is in contact with the weld metal at the mating surface.

3. The welded joint according to claim 2, characterized in that the thickness of the zinc-based plating layer in the first plating thickness reduction portion in contact with the weld metal is 1.0 μm or more and 4.5 μm or less.

4. The zinc-plated metal sheet has a second plated thickness reduction portion between the first plated thickness reduction portion and the weld metal at the mating surface. The thickness of the zinc-based plating layer in the second plated thickness reduction area is less than 1.0 μm. The welded joint according to feature 1.

5. The welded joint according to claim 1, characterized in that the distance W1 between the edge of the first plated thickness reduction portion opposite to the weld metal and the weld metal is 0.35 mm or more and 5.00 mm or less.

6. The welded joint according to claim 4, characterized in that the distance W2 between the edge of the second plating thickness reduction portion opposite to the weld metal and the weld metal is greater than 0 mm and less than or equal to 1.2 mm.

7. The welded joint according to claim 4, characterized in that the difference between the distance W1 between the edge opposite to the weld metal of the first plated thickness reduction portion and the weld metal, and the distance W2 between the edge opposite to the weld metal of the second plated thickness reduction portion and the weld metal, is greater than 0 mm and less than or equal to 3.8 mm.

8. Two or more of the aforementioned metal plates are zinc-plated metal plates, At the joint surface of the two zinc-plated metal plates, the zinc-plated layers of each of the two zinc-plated metal plates are superimposed. In the aforementioned mating surface, each of the two zinc-plated metal plates has the first plate thickness reduction portion. The welded joint according to feature 1.

9. The welded joint according to claim 1, characterized in that the zinc-based plating layer is a ternary plating layer containing Al and Mg, with the remainder being Zn and impurities.

10. The welded joint according to claim 1, characterized in that the thickness of one or more of the metal plates is 0.5 mm or more and 3.0 mm or less.

11. The Vickers hardness of the aforementioned metal plate is between 150 HV and 750 HV. The welded joint according to feature 1.

12. A mechanical structural member comprising a welded joint according to any one of claims 1 to 11.

13. An automobile component comprising a welded joint according to any one of claims 1 to 11.

14. A step of forming a first plating thickness reduction portion on a zinc-plated metal sheet having a zinc-based plating layer on one or both surfaces, A step of stacking multiple metal sheets, including the aforementioned zinc-plated metal sheet, The process of welding the aforementioned metal plate, Equipped with, When forming the first plated thickness reduction portion, the thickness of the zinc-based plating layer in the first plated thickness reduction portion is set to 1.0 μm or more and 30.0 μm or less. When stacking the aforementioned metal plates, at least one of the zinc-based plating layers and the first plating thickness reduction portion are placed on the mating surface. When welding the metal plates, a molten pool is formed inside the outer edge of the first plated thickness reduction portion at the joint surface, and the first plated thickness reduction portion around the outer edge is left in the welded portion. A method for manufacturing welded joints.

15. When forming the first plated thickness reduction portion, a second plated thickness reduction portion is formed inside the first plated thickness reduction portion. When welding the metal plate, the molten pool is formed in the second plate thickness reduction portion at the joint surface. The method for manufacturing a welded joint according to claim 14.

16. The method for manufacturing a welded joint according to claim 15, characterized in that when welding the metal plate, the molten pool is formed on the joint surface so as to cover the entire second plate thickness reduction portion and extend to the first plate thickness reduction portion.

17. The first plated thickness reduction portion is formed by irradiation with a pulsed laser or by cutting. The aforementioned metal plate is welded using a continuous-wave laser. A method for manufacturing a welded joint according to any one of claims 14 to 16.

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