Joint structure, press-formed product, and aluminum-based plated steel sheet

Abstract

A joint structure according to one embodiment of the present disclosure comprises a first press-formed member and a second press-formed member that are made of steel, a welding bead that joins the first press-formed member and the second press-formed member, and a heat affected zone that is present around the welding bead, wherein one or both of the first press-formed member and the second press-formed member have an aluminum-based plating layer on at least one surface thereof, and the average aluminum concentration of the welding bead is 1.0 mass% or less. Preferably, the joint structure has a plating removed portion that extends along the welding bead, between the welding bead and the aluminum-based plating layer.

Description

Joint structures, press-formed products, and aluminum-plated steel sheets

[0001] This disclosure relates to a joint structure, a press-formed product, and an aluminum-plated steel sheet. This application claims priority under Japanese Patent Application No. 2024-182152, filed in Japan on October 17, 2024, the contents of which are incorporated herein by reference.

[0002] Press-formed parts and joint structures obtained by welding multiple press-formed parts are applied to various mechanical structural components. A suitable example of an application for joint structures made of press-formed parts is automotive parts.

[0003] When press-formed products are manufactured by hot stamping, an aluminum-based plating layer may be applied to the surface of the press-formed product. The aluminum-based plating layer suppresses the formation of oxide scale on the surface when the aluminum-plated steel sheet is heated for hot stamping.

[0004] Examples of welding methods for steel plates, or welding methods for press-formed products obtained by press-forming steel plates, are disclosed in Patent Documents 1 to 3.

[0005] Patent No. 5237263 Patent No. 6826999 Patent No. 6495383

[0006] A joint structure obtained by welding press-formed products has a heat-affected zone formed around the weld bead. The strength of the heat-affected zone is lower than that of the base material. Therefore, it is necessary to strengthen the weld bead to compensate for the strength reduction in the heat-affected zone and ensure joint strength.

[0007] As one means of strengthening the weld bead, the inventors considered optimizing the shape of the weld bead. However, in the prior art, no effective means for optimizing the shape of the weld bead of a joint structure has been proposed.

[0008] In view of the above circumstances, the purpose of this disclosure is to provide a joint structure, a press-formed product, and an aluminum-plated steel sheet that can optimize the shape of the weld bead.

[0009] The gist of this disclosure is as follows:

[0010] (1) A joining structure according to one aspect of the present disclosure comprises a first press-formed member and a second press-formed member made of steel, a weld bead joining the first press-formed member and the second press-formed member, and a heat-affected zone present around the weld bead, wherein one or both of the first press-formed member and the second press-formed member have an aluminum-based plating layer on at least one surface, and the average aluminum concentration of the weld bead is Al ＡＶＥ (1) The average aluminum concentration of the weld bead is 1.0% by mass or less. (2) Preferably, in the joining structure described in (1) above, the first press-formed member, the second press-formed member, and the weld bead form an overlap fillet joint, and the weld bead joins the end face of the first press-formed member and the surface of the second press-formed member. (3) Preferably, in the joining structure described in (2) above, when the surface of the first press-formed member opposite to the second press-formed member is defined as the S1a surface, the surface of the first press-formed member on the side of the second press-formed member is defined as the S1b surface, and the surface of the second press-formed member on the side of the first press-formed member is defined as the S2a surface, the average aluminum concentration of the weld bead is Al ＡＶＥ The values ​​M1a, M1b, M2a, W1a, W1b, W2a, and A, which are measured in a cross-section perpendicular to the weld line of the weld bead, satisfy the following formula: Al ＡＶＥ≤ 0.172 × (W1a × M1a + W1b × M1b + W2a × M2a) ÷ A Here, M1a is the thickness in units of mm of the aluminum-based plating layer on the S1a surface, M1b is the thickness in units of mm of the aluminum-based plating layer on the S1b surface, M2a is the thickness in units of mm of the aluminum-based plating layer on the S2a surface, W1a is the distance in units of mm between the intersection point X of the imaginary line along the S1a surface and the surface of the weld bead and the toe of the weld bead on the side of the first press-formed member, W1b is the distance in units of mm between the intersection point Y of the surface of the weld bead and the S1b surface, measured in a direction parallel to the imaginary line and the intersection point X, W2a is the distance in units of mm between the intersection point Z of the surface of the weld bead and the S2a surface and the toe of the weld bead on the side of the second press-formed member, and A is the unit of mm of the weld bead. ２ This is the cross-sectional area. (4) Preferably, in the joining structure described in (2) or (3) above, the penetration depth of the weld bead in the second press-formed member is 50% or more of the thickness of the second press-formed member. (5) Preferably, in the joining structure described in (1) above, the first press-formed member, the second press-formed member, and the weld bead form a T-joint, and the end face of the first press-formed member abuts against the surface of the second press-formed member. (6) Preferably, in the joining structure described in (5) above, when the surface of the first press-formed member on which the weld bead is placed is defined as the S1a surface, and the surface of the second press-formed member on the side of the first press-formed member is defined as the S2a surface, the average aluminum concentration of the weld bead is Al ＡＶＥ The values ​​W1a, W2a, M1a, M2a, and A, which are measured in a cross-section perpendicular to the weld line of the weld bead, satisfy the following formula: Al ＡＶＥ≦ 0.172 × (W1a × M1a + W2a × M2a) ÷ A where M1a is the thickness in mm of the aluminum-based plating layer on the S1a surface, M2a is the thickness in mm of the aluminum-based plating layer on the S2a surface, W1a is the distance in mm between the end on the side of the first press-forming member of the weld bead, measured in a direction parallel to the S1a surface, and the S2a surface, W2a is the distance in mm between the end on the side of the second press-forming member of the weld bead, measured along the S2a surface, and the intersection of the weld bead and the S2a surface on the mating surface of the first press-forming member and the second press-forming member, and A is the cross-sectional area in mm of the weld bead. ２ (7) Preferably, in the joining structure described in (1) above, the first press-forming member, the second press-forming member, and the weld bead form a butt joint. (8) Preferably, in the joining structure described in (7) above, when the surface of the first press-forming member facing the a side, which is one side of the first press-forming member, is defined as the S1a surface, the surface of the second press-forming member facing the a side of the first press-forming member is defined as the S2a surface, the surface of the first press-forming member facing the b side, which is the other side of the first press-forming member, is defined as the S1b surface, and the surface of the second press-forming member facing the b side of the first press-forming member is defined as the S2b surface, the average aluminum concentration Al ＡＶＥ of the weld bead, and Wa, Wb, M1a, M1b, M2a, M2b, and A, which are values measured in a cross-section perpendicular to the welding line of the weld bead, satisfy the following formula. Al ＡＶＥ≤ 0.172 × (Wa ÷ 2 × (M1a + M2a) + Wb ÷ 2 × (M1b + M2b)) ÷ A where M1a is the thickness in units of mm of the aluminum-based plating layer on the S1a surface, M1b is the thickness in units of mm of the aluminum-based plating layer on the S1b surface, M2a is the thickness in units of mm of the aluminum-based plating layer on the S2a surface, M2b is the thickness in units of mm of the aluminum-based plating layer on the S2b surface, Wa is the width in units of mm of the weld bead on the a side of the joint structure, Wb is the width in units of mm of the weld bead on the b side of the joint structure, and A is the width in units of mm of the weld bead ２This is the cross-sectional area. (9) Preferably, in the joining structure described in any one of (1) to (8) above, the joining structure has a plating removal portion extending along the weld bead between the weld bead and the aluminum-based plating layer. (10) Preferably, in the joining structure described in (9) above, the plating removal portion has machining marks or laser ablation marks. (11) Preferably, in the joining structure described in (9) or (10) above, the base steel member is exposed in the plating removal portion, and the plating removal portion has machining marks. (12) Preferably, in the joining structure described in any one of (9) to (11) above, the plating removal portion has heat treatment marks. (13) Preferably, in the joining structure described in any one of (9) to (11) above, the plating removal portion does not have heat treatment marks. (14) Preferably, in the joining structure described in any one of (1) to (13) above, the thickness of the first press-formed member and the second press-formed member is 0.8 to 4.0 mm, and the chemical composition of the base steel members of the first press-formed member and the second press-formed member is, in mass%, C: 0.02% to 0.58%, Mn: 0.20% to 3.00%, Al: 0.005% to 0.060%, P: 0.03% or less, S: 0.010% or less, N: 0.0 10% or less, Ti: 0% to 0.20%, Nb: 0% to 0.20%, V: 0% to 1.0%, W: 0% to 1.0%, Cr: 0% to 1.0%, Mo: 0% to 1.0%, Cu: 0% to 1.0%, Ni: 0% to 1.0%, B: 0% to 0.0100%, Mg: 0% to 0.05%, Ca: 0% to 0.05%, REM: 0% to 0.05%, Sn: 0% to 0.5%, Bi: 0% to 0.05%, Si: 0% to 2.00%, and the remainder: Fe and impurities. (15) Preferably, in the joint structure described in any one of the above items (1) to (14), the average hardness of the weld bead is greater than the minimum hardness of the heat-affected zone. (16) Preferably, in the joining structure described in any one of (1) to (15) above, the average aluminum concentration of the weld bead is 0.17% by mass or more. (17) Preferably, in the joining structure described in any one of (1) to (16) above, the weld bead is an arc weld bead.

[0011] (18) A press-formed article according to another aspect of the present disclosure is a press-formed article for a first press-formed member of a joint structure described in any one of paragraphs (1) to (17) above, wherein it has an aluminum-based plating layer on one or both surfaces, and the aluminum-based plating layer is provided on the surface, wherein a plating removal portion extending to the end of the press-formed article is provided.

[0012] (19) An aluminum-plated steel sheet according to another aspect of the present disclosure is an aluminum-plated steel sheet for manufacturing a press-formed product as described in (18) above, having an aluminum-plated layer on one or both surfaces, wherein the surface on which the aluminum-plated layer is provided is provided with a plating removal portion that extends to the end of the aluminum-plated steel sheet.

[0013] (20) A press-formed article according to another aspect of the present disclosure is a press-formed article for a second press-formed member of a joining structure described in any one of paragraphs (1) to (17) above, wherein one or both surfaces have an aluminum-based plating layer, and a plating removal portion is provided in the welding-scheduled portion of the surface on which the aluminum-based plating layer is provided.

[0014] (21) An aluminum-plated steel sheet according to another aspect of the present disclosure is an aluminum-plated steel sheet for manufacturing a press-formed product as described in (20) above, wherein it has an aluminum-plated layer on one or both surfaces, and a plating removal portion is provided in the welding-planned portion of the surface on which the aluminum-plated layer is provided.

[0015] According to this disclosure, it is possible to provide a joint structure, a press-formed product, and an aluminum-plated steel sheet that can optimize the shape of the weld bead.

[0016] This is a schematic cross-sectional view of an example of a joint structure where the weld is an lap fillet joint. This is a schematic cross-sectional view of an example of a joint structure where the weld is a T-joint. This is a schematic cross-sectional view of an example of a joint structure where the weld is a butt joint. This is a perspective view of an example of a joint structure where the press-formed members are a hat-shaped member and a plate-shaped member. This is a perspective view of an example of a joint structure where both press-formed members are hat-shaped members. This is a perspective view of an example of a joint structure where the press-formed members are a hat-shaped member and a plate-shaped member. This is a cross-sectional trace of a weld bead with an average aluminum concentration of 1.0 mass% or less. This is a cross-sectional trace of a weld bead with an average aluminum concentration of more than 1.0 mass%. This is an enlarged view of the root portion of the lap fillet joint in Figure 1. This is a perspective view of a weld with a plate removal portion. This is a perspective view of a press-formed product with a plate removal portion. This is an example of a second press-formed product. This is an example of a second press-formed product. This is an example of a second press-formed product. This is an example of a first aluminum-plated steel sheet. This is an example of a second aluminum-plated steel sheet. This is an example of a second aluminum-plated steel sheet.

[0017] The inventors diligently investigated means to optimize the shape of the weld bead of a joint structure. As a result, the inventors discovered that the aluminum-based plating layer on the press-formed product, which is the material of the joint structure, affects the shape of the weld bead. For example, the inventors found that when press-formed products of a joint structure are subjected to lap fillet welding, the aluminum-based plating layer tends to widen the weld bead and decrease the penetration depth of the weld bead. Furthermore, the inventors found that by removing the aluminum-based plating layer from the area to be welded on the press-formed product before performing lap fillet welding, the amount of aluminum-based plating layer that penetrates into the weld bead is reduced, thereby optimizing the shape of the weld bead.

[0018] (1. Joining Structure 1) Based on the above findings, a joining structure 1 according to one embodiment of the present disclosure comprises a first press-formed member 11 and a second press-formed member 12 made of steel, a weld bead 131 joining the first press-formed member 11 and the second press-formed member 12, and a heat-affected zone 132 present around the weld bead 131, wherein one or both of the first press-formed member 11 and the second press-formed member 12 have an aluminum-based plating layer on at least one surface, and the average aluminum concentration of the weld bead 131 is 1.0 mass% or less. The details of the joining structure 1 according to this embodiment will be described below with reference to the drawings.

[0019] (Joint structure 1) Joint structure 1 comprises a first press-formed member 11 made of steel and a second press-formed member 12 made of steel. The first press-formed member 11 and the second press-formed member 12 are welded to each other. Both press-formed members are manufactured by press-forming steel plates.

[0020] The first press-formed member 11 and the second press-formed member 12 are defined as follows: (1) In a joint structure where the welded portion 13 is an overlap fillet joint, as illustrated in Figure 1, the member whose end face is joined to another member is considered the first press-formed member 11, and the member whose surface is joined to another member is considered the second press-formed member 12. (2) In a joint structure where the welded portion 13 is a T-joint, as illustrated in Figure 2, the member whose end face rests on another member is considered the first press-formed member 11, and the member whose surface is joined to another member is considered the second press-formed member 12. (3) In a joint structure where the welded portion 13 is a butt joint, as illustrated in Figure 3, any one of the members is considered the first press-formed member 11, and the other member is considered the second press-formed member 12. There is no need to distinguish between the two press-formed members.

[0021] Details of lap fillet joints, T-joints, and butt joints will be described later. In this disclosure, the term "welded area 13" refers to the portion including the weld bead 131 and the heat-affected zone 132.

[0022] Various shapes can be applied to the joint structure 1. Examples of shapes of the joint structure 1 are shown in Figures 4 to 6. In the row of joint structure 1 in Figures 4 to 6, at least one of the press-formed members is a hat-shaped member. A hat-shaped member is a member formed by bending a steel plate. A hat-shaped member has, for example, a top plate A, a flange B, and a side plate C. The top plate A, flange B, and side plate C are all plate-like parts having a substantially rectangular shape. The flange B and side plate C are arranged on both sides of the top plate A. The flange B is substantially parallel to the top plate A and is located at both ends of the hat-shaped member. The side plate C is located between the top plate A and the flange B and forms a predetermined angle with respect to the top plate A and flange B.

[0023] In the joint structure 1 shown in Figure 4, one press-formed member is a hat-shaped member, and the other press-formed member is a plate-shaped member. In the joint structure 1 shown in Figure 4, the end face of the flange portion B of the hat-shaped member and the surface of the plate-shaped member are joined by a weld bead 131. The welded portion 13 in the joint structure 1 shown in Figure 4 is a lap fillet joint. In the joint structure 1 shown in Figure 4, the hat-shaped member corresponds to the first press-formed member 11, and the plate-shaped member corresponds to the second press-formed member 12.

[0024] In the joint structure 1 shown in Figure 5, both press-formed members are hat-shaped members. The two hat-shaped members are stacked on top of each other. The end face perpendicular to the longitudinal direction of one hat-shaped member and the surface of the other hat-shaped member are joined by a weld bead 131. The weld in the joint structure 1 shown in Figure 5 is a fillet joint. In the joint structure 1 shown in Figure 5, the hat-shaped member on the upper side of the paper corresponds to the first press-formed member 11, and the hat-shaped member on the lower side of the paper corresponds to the second press-formed member 12.

[0025] In the joining structure 1 of Figure 6, one press-formed member is a hat-shaped member, and the other press-formed member is a plate-shaped member. The plate-shaped member is superimposed on the top plate portion A of the hat-shaped member. The end face of the plate-shaped member is joined to the surface of the top plate portion A of the hat-shaped member over its entire length. In the joining structure 1 of Figure 6, the plate-shaped member corresponds to the first press-formed member 11, and the hat-shaped member corresponds to the second press-formed member 12.

[0026] The welded joint 13 of the joint structure 1 illustrated in Figures 4 to 6 is a lap fillet joint. However, the welded joint 13 of the joint structure 1 according to this embodiment is not limited to a lap fillet joint. As described above, the welded joint 13 of the joint structure 1 according to this embodiment can also be a T-joint or a butt joint.

[0027] (Weld bead 131 and heat-affected zone 132) The first press-formed member 11 and the second press-formed member 12 are joined by a weld bead 131. The weld bead 131 may be an arc weld bead produced by arc welding or a laser weld bead produced by laser welding. The type of weld bead can be determined by observing the shape of its surface and cross-section. The term "cross-section" means a cross-section perpendicular to the direction in which the weld bead extends. When producing the weld bead 131, filler material may be added to the molten pool. The weld bead 131 may contain components of the filler material.

[0028] In the weld bead 131, the first press-formed member 11 and the second press-formed member 12 are melted and solidified. In addition, a heat-affected zone 132 exists around the weld bead 131. The heat-affected zone 132 is the unmelted portion of the base material where the structure, metallurgical properties, and mechanical properties have changed due to the heat from welding, cutting, etc. The heat-affected zone 132 is sometimes referred to as the HAZ.

[0029] Generally, softening occurs in the heat-affected zone 132. Therefore, the heat-affected zone 132 may reduce the joint strength of the welded portion 13. In the prior art, various methods have been considered to compensate for the reduction in joint strength due to the heat-affected zone 132. For example, post-heat treatment may be performed on the welded portion 13 to eliminate the heat-affected zone 132. Alternatively, the heat-affected zone 132 can be eliminated by butt welding steel plates together to form a tailored blank and then hot stamping. The heat-affected zone 132 formed on the tailored blank before hot stamping becomes invisible in the press-formed product after hot stamping, even after etching to reveal the cross-sectional structure. However, post-heat treatment increases the manufacturing cost of the joint structure 1. Furthermore, there are many parts that must be joined after forming. Therefore, in the joint structure 1 according to this embodiment, the reduction in joint strength due to the heat-affected zone 132 is compensated for by means other than heat treatment.

[0030] (Aluminum-based plating layer and base steel member) One or both of the first press-formed member 11 and the second press-formed member 12 have an aluminum-based plating layer on at least one surface. That is, at least one of the first press-formed member 11 and the second press-formed member 12 is an aluminum-based plated steel member. The first press-formed member 11, which is made of an aluminum-based plated steel sheet, has a base steel member 111 and an aluminum-based plating layer 112 provided on at least one surface of the base steel member 111. Similarly, the second press-formed member 12, which is made of an aluminum-based plated steel sheet, has a base steel member 121 and an aluminum-based plating layer 122 provided on at least one surface of the base steel member 121.

[0031] The aluminum-based plating layer prevents corrosion of the base steel component. Furthermore, the aluminum-based plating layer prevents the formation of oxide scale on the surface of press-formed products during the manufacturing process.

[0032] The aluminum-based plating layer is a plating layer mainly containing aluminum, and it only needs to contain 50% by mass or more of aluminum. Depending on the purpose, the aluminum-based plating layer may contain elements other than aluminum such as Si. The aluminum-based plating layer may contain impurities that are mixed in during the manufacturing process or the like.

[0033] Specifically, for example, the aluminum-based plating layer may have a chemical composition containing 5% to 12% of Si (silicon) in mass%, and the balance being aluminum and impurities. Also, the aluminum-based plating layer may have a chemical composition containing 5% to 12% of Si (silicon) and 2% to 4% of Fe (iron) in mass%, and the balance being aluminum and impurities. When Si is contained in the aluminum-based plating layer within the above range, the reduction in workability and corrosion resistance can be suppressed. Also, when Si is contained in the aluminum-based plating layer within the above range, the thickness of the intermetallic compound layer can be reduced. The intermetallic compound layer is a layer that may be formed inside the aluminum-based plating layer and in contact with the base steel member.

[0034] Due to heating during molten plating and hot press forming, the aluminum-based plating layer can alloy with Fe in the base steel plate. Therefore, the aluminum-based plating layer is not necessarily formed as a single layer with a constant component composition. For example, the aluminum-based plating layer may contain an intermetallic compound layer that is a partially alloyed layer.

[0035] In FIGS. 1 to 3, for the convenience of explanation, the aluminum-based plating layers 112 and 122 are depicted as being very thick. However, in reality, the thicknesses of the aluminum-based plating layers 112 and 122 are often much smaller than those of the base steel members 111 and 121. The average thickness of the aluminum-based plating layers 112 and 122 is, for example, 8 μm or more, or 15 μm or more. The average thickness of the aluminum-based plating layers 112 and 122 is, for example, 40 μm or less, 35 μm or less, or 30 μm or less.

[0036] (Average aluminum concentration of weld bead 131) The average aluminum concentration of the weld bead 131 is 1.0 mass% or less. Preferably, the average aluminum concentration of the weld bead 131 is 0.9 mass% or less, 0.8 mass% or less, or 0.7 mass% or less. The lower limit of the average aluminum concentration of the weld bead 131 is not particularly limited. For example, it is preferable that the average aluminum concentration of the weld bead 131 be 0.20 mass% or more, 0.17 mass% or more, 0.15 mass% or more, or 0.10 mass% or more.

[0037] "Average aluminum concentration" refers to the average value of the aluminum concentration measured across the entire cross-section of the weld bead 131. The aluminum concentration in the weld bead 131 is not uniform. For example, aluminum segregation may occur near the toes 1311 and 1312 of the weld bead 131. Therefore, when evaluating the amount of aluminum in the weld bead 131, the average value of the aluminum concentration is measured.

[0038] The method for measuring the average aluminum concentration of the weld bead 131 is as follows. First, the weld portion 13 is cut perpendicular to the extension direction of the weld bead 131 and embedded in resin. The cross-section of the embedded sample is polished. The cross-section of the weld bead 131 is mapped and analyzed using an electron beam microanalyzer (FE-EPMA) to measure the aluminum concentration. The measurement conditions are as follows: Acceleration voltage: 15 kV Beam diameter: approximately 100 nm Irradiation time: 1000 ms Measurement points are arranged in a grid pattern on the cross-section of the weld bead 131. The interval between measurement points is 5 μm. The arithmetic mean of the measured aluminum concentration at all measurement points is considered to be the average aluminum concentration (in mass%) of the weld bead 131. This type of cross-sectional analysis is performed at five locations. The positions of the cross-sections to be analyzed are evenly distributed on the weld bead.

[0039] (Effects) In welding press-formed members obtained by hot stamping aluminum-plated steel sheets, the joint strength may decrease due to poor shape of the weld bead 131. For example, if the welding is a downward fillet arc weld, the penetration depth of the second press-formed member 12, which is the lower plate, tends to be insufficient.

[0040] On the other hand, in the joining structure 1 according to this embodiment, the average aluminum concentration of the weld bead 131 is set to 1.0 mass% or less. This makes it possible to optimize the shape of the weld bead 131.

[0041] Figure 7 shows a cross-sectional trace of the weld bead 131 of the joint structure 1 according to this embodiment, and Figure 8 shows a cross-sectional trace of the weld bead 431 of a conventional joint structure 1. In both joint structures 1, the first press-formed member 11, which is the upper plate, and the second press-formed member 12, which is the lower plate, were made of aluminum-plated steel. The chemical composition of the aluminum-plated layer was such that it contained 5% to 12% Si and 2% to 4% Fe by mass, with the remainder being aluminum and impurities. The aluminum-plated layer was applied to both sides of the upper plate and both sides of the lower plate. The welding conditions for these weld beads 131 were as follows.

[0042]

[0043] In Figures 7 and 8, the penetration depth of the weld bead 131 is indicated by the symbol P. Generally, the greater the welding current and welding voltage, the greater the penetration depth. The welding current and welding voltage for the weld bead 131 in Figure 7 were smaller than those for the weld bead 431 in Figure 8. Therefore, based on conventional knowledge, it would be expected that the penetration depth of the weld bead 131 in Figure 7 would be smaller than that of the weld bead 431 in Figure 8. However, contrary to expectations, the penetration depth of the weld bead 131 in Figure 7 was much greater than that of the weld bead 431 in Figure 8. The penetration depth of the weld bead 131 in Figure 7 was approximately 1.8 times that of the weld bead 431 in Figure 8.

[0044] The manufacturing conditions for the weld bead 131 in Figure 7 differed from those for the weld bead 431 in Figure 8, in that the aluminum-based plating layer was removed before welding. When manufacturing the weld bead 131 in Figure 7, first, the aluminum-based plating layer was removed from the entire area of ​​the region where the weld bead 131 was to be made on the upper plate, excluding the tip of the plate, and from the entire area of ​​the region where the weld bead 131 was to be made on the lower plate, until the base steel plate was exposed. Then, the upper and lower plates were fillet arc welded. As a result, the average aluminum concentration of the weld bead 131 in Figure 7 was reduced. On the other hand, when manufacturing the weld bead 431 in Figure 8, the upper and lower plates were fillet arc welded without removing the aluminum-based plating layer. Therefore, the aluminum-based plating layers of the upper plate (first press-formed member 41) and the lower plate (second press-formed member 42) dissolved into the weld bead 431 in Figure 8, and the average aluminum concentration of the weld bead 431 increased.

[0045] The reason why the aluminum concentration in the weld bead 131 affects its shape is not currently clear. The inventors hypothesize that the lower the average aluminum concentration in the molten pool, the more likely Marangoni convection is to occur in the molten pool from the toe to the center. The width of the weld bead 131 in Figure 7, i.e., the length of the weld bead 131 along the horizontal direction of the paper, is smaller than that of the weld bead 431 in Figure 8. The inventors hypothesize that when the weld bead 131 in Figure 7 was formed, the width of the molten pool and the weld bead 131 was narrowed and the penetration depth P was expanded due to Marangoni convection. It should be noted that optimizing the shape of the weld bead 131 by reducing the average aluminum concentration of the weld bead 131 can also be achieved in welded joints other than lap fillet welds.

[0046] By optimizing the shape of the weld bead 131, the weld bead 131 is strengthened. From the viewpoint of plastic constraint, strengthening the weld bead 131 can suppress the decrease in joint strength due to the softening of the heat-affected zone 132. Therefore, the joint structure 1 according to this embodiment has high joint strength.

[0047] Furthermore, in the joint structure 1 according to this embodiment, the welding heat input required to ensure penetration depth is small. By reducing the welding heat input, spatter scattering and burn-through can be suppressed. Moreover, by reducing the welding heat input while maintaining the penetration depth, the width of the softened region in the heat-affected zone 132 can be narrowed, and the joint strength can be further increased. For example, when the first press-formed member, the second press-formed member, and the weld bead form an overlapping fillet joint, it is preferable that the penetration depth of the weld bead in the second press-formed member be 50% or more, 60% or more, or 70% or more of the thickness of the second press-formed member. In the joint structure 1 according to this embodiment, even when the penetration depth is increased to 50% or more, the width of the softened region can be narrowed. The upper limit of the penetration depth of the weld bead in the second press-formed member is not particularly limited, but for example, this value may be 100% or less, 90% or less, 80% or less, or 75% or less.

[0048] The most basic embodiment of the joint structure 1 according to this embodiment has been described above. Preferred embodiments will be described below.

[0049] Various shapes can be applied to the welded joint 13 of the joint structure 1. Preferred examples of the shapes of the welded joint 13 are the lap fillet joint, T-joint, and butt joint described above. Joint structures 1 to which these joint structures are applied will be described in detail below.

[0050] (Lag Fillet Joint) The first press-formed member 11, the second press-formed member 12, and the weld bead 131 can form a lap fillet joint. In this disclosure, the term "lap fillet joint" means a fillet-welded lap joint. The term "fillet joint" means a joint having a triangular cross-section formed by welding two substantially orthogonal surfaces. The term "lap joint" means a joint in which, in a cross-section perpendicular to the weld line, the parts are placed at an angle of approximately 0 degrees ≤ α ≤ 30 degrees (where α is the angle between the surfaces of the parts) and overlap each other.

[0051] Figure 1 shows a schematic cross-sectional view of an overlap fillet joint. In an overlap fillet joint, a weld bead 131 joins the end face of the first press-formed member 11 and the surface of the second press-formed member 12. The first press-formed member 11 and the second press-formed member 12 are overlapped around the weld bead 131. The weld bead 131 joins two substantially orthogonal surfaces, namely the end face of the first press-formed member 11 and the surface of the second press-formed member 12.

[0052] Furthermore, the first press-formed member 11 and the second press-formed member 12 do not need to be in complete contact at their mating surfaces. As illustrated in the enlarged cross-sectional view of Figure 9, there may be a small gap between the first press-formed member 11 and the second press-formed member 12. Also, the first press-formed member 11 and the second press-formed member 12 do not need to be perfectly parallel around the weld bead 131.

[0053] In the joint structure 1 where the welded joint 13 is an overlap fillet joint, the average aluminum concentration of the weld bead 131 is Al ＡＶＥ Furthermore, it is preferable that the values ​​M1a, M1b, M2a, W1a, W1b, and W2a, measured in a cross-section perpendicular to the weld line of the weld bead 131, satisfy the following formula. ＡＶＥ ≤ 0.172 × (W1a × M1a + W1b × M1b + W2a × M2a) ÷ A

[0054] Here, the definitions of the symbols and other terms included in the above formula are as follows: The units of W1a, M1a, W2a, and M2a are mm, and the unit of A is mm. ２: S1a surface (reference numeral S1a in Figure 1): The surface of the first press-formed member 11 opposite to the second press-formed member 12 S1b surface (reference numeral S1b in Figure 1): The surface of the first press-formed member 11 on the side of the second press-formed member 12 S2a surface (reference numeral S2a in Figure 1): The surface of the second press-formed member 12 on the side of the first press-formed member 11 M1a: Thickness of the aluminum-based plating layer 112 on the S1a surface M1b: Thickness of the aluminum-based plating layer 112 on the S1b surface M2a: Thickness of the aluminum-based plating layer 122 on the S2a surface W1a: Distance between the intersection point X of the imaginary line VL along the S1a surface and the surface of the weld bead 131 and the toe end 1311 on the side of the first press-formed member 11 of the weld bead 131 W1b: Distance between intersection point Y (see Figure 9) of the surface of the weld bead 131 and the S1b surface, measured in a direction parallel to the imaginary line VL, and intersection point X. W2a: Distance between intersection point Z (see Figure 9) of the surface of the weld bead 131 and the S2a surface, and the toe end 1312 on the side of the second press-formed member 12 of the weld bead 131. A: Cross-sectional area of ​​the weld bead 131.

[0055] The symbols M1a, M1b, and M2a indicate the thickness of the aluminum-based plating layer. If no aluminum-based plating layer is present, its thickness is considered to be 0. For example, if the aluminum-based plating layer 112 is not present on the S1a surface, M1a is 0. Furthermore, the thicknesses M1a, M1b, and M2a of the aluminum-based plating layer are values ​​measured outside the plating removal section 14, which will be described later.

[0056] The symbols W1a, W1b, and W2a are values ​​determined based on the shape of the weld bead 131 and the welded portion 13, and are estimated widths of the aluminum-based plating layers 112 and 122 incorporated into the weld bead 131. The details of the symbols W1a, W1b, and W2a will be explained below with reference to the schematic cross-sectional view of the lap fillet joint shown in Figure 1 and the enlarged view of the root portion 1313 shown in Figure 9. The root portion 1313 of the lap fillet joint shown in Figures 1 and 9 is the region where the mating surfaces of the first press-formed member 11 and the second press-formed member 12 intersect with the surface of the weld bead 131. Note that a gap may occur between the first press-formed member 11 and the second press-formed member 12 at the mating surface. Therefore, the root portion 1313 may exist as a region rather than a point in the cross-section.

[0057] Figures 1 and 9 show cross-sections of the weld bead 131 perpendicular to the weld line. The weld line is a virtual line when the weld bead 131 is represented as a single line. The determination of whether the joint structure 1 satisfies the above formula is made at a cross-section perpendicular to the weld line of the weld bead 131. M1a, M1b, M2a, W1a, W1b, and W2a are measured at this cross-section. In this disclosure, unless otherwise specified, "cross-section" means a cross-section of the weld bead 131 perpendicular to the weld line.

[0058] (W1a of overlap fillet joint) W1a of the overlap fillet joint is the distance between the intersection point X of the imaginary line VL along the S1a plane and the surface of the weld bead 131 and the toe 1311 on the side of the weld bead 131 on the first press-formed member 11. The term "toe" refers to the point where the surface of the base material and the surface of the weld bead 131 intersect. The toe 1311 on the side of the weld bead 131 on the first press-formed member 11 is the intersection point of the S1a plane and the surface of the weld bead 131. The toe 1312 on the side of the weld bead 131 on the second press-formed member 12, as described later, is the intersection point of the S2a plane and the surface of the weld bead 131.

[0059] The intersection point X may coincide with the toe 1311 on the side of the first press-formed member 11. If the weld bead 131 is recessed downwards in the plane of the paper, the imaginary line VL and the surface of the weld bead 131 do not intersect. In this case, the toe 1311 on the side of the weld bead 131 on the first press-formed member 11 is considered to be the intersection point X, and W1a is considered to be 0 mm. On the other hand, as shown in the schematic cross-sectional view of Figure 1, if the weld bead 131 is raised above the S1a surface, the imaginary line VL and the surface of the weld bead 131 intersect. In this case, the intersection point X between the imaginary line VL and the surface of the weld bead 131 does not coincide with the toe 1311 on the side of the first press-formed member 11, and W1a is greater than 0 mm.

[0060] The imaginary line VL along the surface S1a is the estimated position of the surface S1a before the weld bead 131 is formed. The intersection point X between the imaginary line VL and the surface of the weld bead 131 is the estimated position of the end face of the first press-formed member 11 before the weld bead 131 is formed.

[0061] W1a of the lap fillet joint is an estimated value of the width of the aluminum-based plating layer 112 on the S1a surface that has fused into the weld bead 131. W1a × M1a is an estimated value of the cross-sectional area of ​​the aluminum-based plating layer 112 on the S1a surface that has fused into the weld bead 131.

[0062] (W1b of lap fillet joint) W1b of the lap fillet joint is the distance between the intersection point Y of the surface of the weld bead 131 and the S1b surface and the intersection point X, measured in a direction parallel to the dashed line VL. The intersection point Y of the surface of the weld bead 131 and the S1b surface is shown in Figure 9.

[0063] As shown in Figure 9, a gap may occur at the mating surface of the first press-formed member 11 and the second press-formed member 12. If the gap is large, W1b is measured with respect to the intersection Y between the surface of the weld bead 131 and the S1b surface. However, if the gap in the root portion 1313 is small, the mating surface of the first press-formed member 11 and the second press-formed member 12 may be visible as a single line in the cross-sectional photograph. In this case, the intersection point between the mating surface and the surface of the weld bead 131 may be considered as intersection Y.

[0064] The distance W1b between intersection point X and intersection point Y, measured along the imaginary line VL, is an estimated value of the width of the aluminum-based plating layer 112 on the S1b surface that has fused into the weld bead 131. W1b × M1b is an estimated value of the cross-sectional area of ​​the aluminum-based plating layer 112 on the S1b surface that has fused into the weld bead 131.

[0065] (W2a of the lap fillet joint) W2a of the lap fillet joint is the distance between the intersection Z of the surface of the weld bead 131 and the S2a surface and the toe 1312 on the side of the second press-formed member 12 of the weld bead 131. The intersection Z of the surface of the weld bead 131 and the S2a surface is shown in Figure 9.

[0066] W2a is measured with reference to the intersection Z between the surface of the weld bead 131 and the surface S2a. However, if the gap in the root portion 1313 is small, the mating surfaces of the first press-formed member 11 and the second press-formed member 12 may be visible as a single line in the cross-sectional photograph. In this case, the intersection point between the mating surface and the surface of the weld bead 131 may be considered as intersection Z. In this case, intersection Y and intersection Z are considered to be in the same position.

[0067] W2a of the lap fillet joint is an estimated value of the width of the aluminum-based plating layer 122 on the S2a surface that has fused into the weld bead 131. W2a × M2a is an estimated value of the cross-sectional area of ​​the aluminum-based plating layer 122 on the S2a surface that has fused into the weld bead 131.

[0068] In the above formula, W1a × M1a + W1b × M1b + W2a × M2a is an estimated value of the total cross-sectional area of ​​the aluminum-based plating layers 112 and 122 that have penetrated into the weld bead 131. (W1a × M1a + W1b × M1b + W2a × M2a) ÷ A is an estimated value of the area ratio of the aluminum-based plating layer in the weld bead 131.

[0069] The coefficient "0.172" in the above formula is the value calculated using the following procedure: 0.172 = (2.71 / 7.87) / 2. The "2.71" in the above formula is in units of g / cm³. ３ The Al density is "7.87", and the unit is g / cm³. ３ This is the density of the weld metal. "0.172" is the value obtained by multiplying the specific gravity conversion value by 50%.

[0070] The welded joint 13 is an overlap fillet joint, and Al ＡＶＥ In a joint structure 1 that satisfies ≤0.172 × (W1a × M1a + W1b × M1b + W2a × M2a) ÷ A, the aluminum-based plating layers 112 and 122 are thicker outside the welded portion 13, while the average aluminum concentration of the weld bead 131 is reduced. This makes it possible to optimize the shape of the weld bead 131 while ensuring the scale prevention effect and corrosion resistance improvement effect of the aluminum-based plating layers 112 and 122. For example, as shown in Figure 11, a joint structure 1 that satisfies the above formula can be obtained by removing the aluminum-based plating layer at the position where the weld bead 131 will be placed before forming the weld bead 131.

[0071] In the lap fillet joint shown in Figure 1, the weld bead 131 does not penetrate the second press-formed member 12. However, the weld bead 131 may penetrate the second press-formed member 12. In lap fillet welding, the phenomenon of the weld bead penetrating the lower plate is called burn-through. In the joint structure 1 according to this embodiment, a small amount of burn-through is acceptable.

[0072] If the welded joint 13 is an overlap fillet joint and the weld bead 131 penetrates the second press-formed member 12, the joint structure 1 may satisfy the following equation: Al ＡＶＥ ≤0.172 × (W1a × M1a + W1b × M1b + W2a × M2a + W2b × M2b) ÷ A Here, the definitions of the signs included in the above formula are as follows: The definitions of signs other than M2b and W2b are as described above. S2b surface: The surface of the second press-formed member 12 opposite to the first press-formed member 11 M2b: The thickness of the aluminum-based plating layer 122 on the S2b surface W2b: The width in units of mm of the weld bead 131 on the S2b surface

[0073] The width of the weld bead 131 on the S2b surface is the width of the weld bead 131 that penetrates the second press-formed member 12 and is exposed on the S2b surface. The surface of the weld bead 131 and the S2b surface intersect at two points. The distance between the two intersection points of the surface of the weld bead 131 and the S2b surface, as measured in cross-section, is W2b.

[0074] If the weld bead 131 penetrates the second press-formed member 12, the aluminum-based plating layer 122 on the S2b surface may also affect the average aluminum concentration of the weld bead 131. Therefore, it is even more preferable to evaluate the relationship between the average aluminum concentration of the weld bead 131 and the thickness of the aluminum-based plating layers 112 and 122 using an equation that takes into account the aluminum-based plating layer 122 on the S2b surface.

[0075] (T-joint) The first press-formed member 11, the second press-formed member 12, and the weld bead 131 can also form a T-joint. The term "T-joint" refers to a joint formed by placing the end face of one plate on the surface of another plate, resulting in a T-shaped joint with approximately right angles.

[0076] Figure 2 shows a schematic cross-sectional view of a T-joint. In the T-joint, the first press-formed member 11 and the second press-formed member 12 are arranged to be approximately perpendicular to each other around the weld bead 131. In the T-joint, the end face of the first press-formed member 11 abuts against the surface of the second press-formed member 12. The weld bead 131 of the T-joint joins the end surface of the first press-formed member 11 to the surface of the second press-formed member 12. The T-joint in Figure 2 is a type of fillet joint.

[0077] Furthermore, it is not necessary for the first press-formed member 11 and the second press-formed member 12 to be perfectly perpendicular around the weld bead 131 of the T-joint. A joint in which the angle between the first press-formed member 11 and the second press-formed member 12 is between 70 degrees and 110 degrees is considered a T-joint.

[0078] In the joint structure 1 where the welded joint 13 is a T-joint, the average aluminum concentration of the weld bead 131 is Al ＡＶＥ Furthermore, it is preferable that the values ​​M1a, M2a, W1a, and W2a measured in a cross-section perpendicular to the weld line of the weld bead 131 satisfy the following formula. ＡＶＥ ≤ 0.172 × (W1a × M1a + W2a × M2a) ÷ A

[0079] Here, the definitions of the symbols and other terms included in the above formula are as follows: The units of W1a, M1a, W2a, and M2a are mm, and the unit of A is mm. ２: S1a surface (reference numeral S1a in Figure 2): The surface of the first press-formed member 11 on the side where the weld bead 131 is located S2a surface (reference numeral S2a in Figure 2): The surface of the second press-formed member 12 on the side of the first press-formed member 11 M1a: Thickness of the aluminum-based plating layer 112 on the S1a surface M2a: Thickness of the aluminum-based plating layer 122 on the S2a surface W1a: Distance measured in a direction parallel to the S1a surface between the toe 1311 of the weld bead 1311 on the side of the first press-formed member 11 and the S2a surface W2a: Distance measured along the S2a surface between the toe 1312 of the weld bead 1311 on the side of the second press-formed member and the intersection point of the weld bead 131 and the S2a surface at the joint surface of the first press-formed member 11 and the second press-formed member 12 A: Cross-sectional area of ​​the weld bead 131

[0080] In this disclosure, the surface of the first press-formed member 11 of the T-joint opposite to the S1a surface is referred to as the S1b surface, and the surface of the second press-formed member 12 opposite to the S2a surface is referred to as the S2b surface.

[0081] The symbols M1a and M2a indicate the thickness of the aluminum-based plating layer. If no aluminum-based plating layer is present, its thickness is considered to be 0 mm. For example, if no aluminum-based plating layer 112 is present on the S1a surface, M1a is 0. The thicknesses M1a and M2a of the aluminum-based plating layers 112 and 122 are values ​​measured outside the plating removal section 14, which will be described later.

[0082] The symbols W1a and W2a are values ​​determined based on the shape of the weld bead 131 and the member, and are estimated widths of the aluminum-based plating layers 112 and 122 incorporated into the weld bead 131. The details of symbols W1a and W2a will be explained below with reference to the schematic cross-sectional view of the T-joint shown in Figure 2.

[0083] (W1a of T-joint) W1a of the T-joint is the distance between the toe 1311 on the side of the first press-formed member 11 of the weld bead 131 and the S2a surface, measured in a direction parallel to the S1a surface. W1a of the T-joint is an estimated value of the width of the aluminum-based plating layer 112 on the S1a surface that has fused into the weld bead 131. W1a × M1a is an estimated value of the cross-sectional area of ​​the aluminum-based plating layer 112 on the S1a surface that has fused into the weld bead 131.

[0084] (W2a of T-joint) W2a of the T-joint is the distance measured along the S2a plane from the toe 1312 of the weld bead 131 on the side of the second press-formed member to the intersection point of the weld bead 131 and the S2a plane at the mating surface of the first press-formed member 11 and the second press-formed member 12. In this disclosure, the root portion 1313 of the T-joint is the region where the mating surface of the first press-formed member 11 and the second press-formed member 12 intersects with the surface of the weld bead 131. The "intersection point of the weld bead 131 and the S2a plane at the mating surface of the first press-formed member 11 and the second press-formed member 12" is the intersection point of the weld bead 131 and the S2a plane at the root portion 1313.

[0085] W2a of the T-joint is an estimated value of the width of the aluminum-based plating layer 122 on the S2a surface that has fused into the weld bead 131. W2a × M2a is an estimated value of the cross-sectional area of ​​the aluminum-based plating layer 122 on the S2a surface that has fused into the weld bead 131.

[0086] In the above formula, W1a × M1a + W2a × M2a is an estimated value of the total cross-sectional area of ​​the aluminum-based plating layers 112 and 122 that have penetrated into the weld bead 131. (W1a × M1a + W2a × M2a) ÷ A is an estimated value of the area ratio of the aluminum-based plating layers 112 and 122 in the weld bead 131.

[0087] The coefficient "0.172" in the above formula is the value obtained by multiplying the specific gravity conversion value by 50%, and its technical significance is as described above in relation to lap fillet joints.

[0088] The welded joint 13 is a T-joint, and Al ＡＶＥIn a joint structure 1 that satisfies ≤0.172 × (W1a × M1a + W2a × M2a) ÷ A, the aluminum-based plating layers 112 and 122 are thicker outside the welded portion 13, while the average aluminum concentration of the weld bead 131 is reduced. This allows for the optimization of the shape of the weld bead 131 while ensuring the scale prevention effect and corrosion resistance improvement effect of the aluminum-based plating layers 112 and 122. By removing the aluminum-based plating layer at the location where the weld bead 131 will be placed before forming the weld bead 131, a joint structure 1 that satisfies the above formula can be obtained.

[0089] (Butt joint) The first press-formed member 11, the second press-formed member 12, and the weld bead 131 can also form a butt joint. The term "butt joint" refers to a joint in which parts placed on the same plane face each other at an angle of 135 degrees ≤ α ≤ 180 degrees (where α is the angle between the surfaces of the parts).

[0090] A schematic cross-sectional view of a butt joint is shown in Figure 3. In a butt joint, a weld bead 131 joins the end face of the first press-formed member 11 to the end face of the second press-formed member 12. In a butt joint, the two members are not distinguished. Therefore, any member can be considered as the first press-formed member 11. In Figure 3, for convenience, the member on the left side of the page is considered as the first press-formed member 11.

[0091] In the joint structure 1 where the welded joint 13 is a butt joint, the average aluminum concentration of the weld bead 131 is Al ＡＶＥ Furthermore, it is preferable that the values ​​M1a, M1b, M2a, M2b, Wa, and Wb, measured in a cross-section perpendicular to the weld line of the weld bead 131, satisfy the following formula. ＡＶＥ ≦0.172×(Wa÷2×(M1a+M2a)+Wb÷2×(M1b+M2b))÷A

[0092] The definitions of the signs and other terms included in the above formula are as follows: The units of Wa, M1a, M2a, Wb, M1b, and M2b are mm. The unit of A is mm. ２: S1a surface (reference numeral S1a in Figure 3): Surface of the first press-formed member 11 on one side (a side) of the joint structure 1 S1b surface (reference numeral S1b in Figure 3): Surface of the first press-formed member 11 on the other side (b side) of the joint structure 1 S2a surface (reference numeral S2a in Figure 3): Surface of the second press-formed member 12 on one side (a side) of the joint structure 1 S2b surface (reference numeral S2b in Figure 3): Other surface of the second press-formed member 12 on the other side (b side) of the joint structure 1 M1a: Thickness of the aluminum-based plating layer 112 on the S1a surface M1b: Thickness of the aluminum-based plating layer 112 on the S1b surface M2a: Thickness of the aluminum-based plating layer 122 on the S2a surface M2b: Thickness of the aluminum-based plating layer 122 on the S2b surface Wa: Width of the weld bead 131 on one side (a side) of the joint structure 1 Wb: Width of the weld bead 131 on the other side (side b) of the joint structure 1. A: Cross-sectional area of ​​the weld bead 131.

[0093] In a butt joint, the front and back surfaces are not distinguished. Therefore, any side of the joint structure 1 can be considered as side a, the surface of the first press-formed member 11 on side a can be considered as S1a, and the surface of the second press-formed member 12 on side a can be considered as S2a. Also, the opposite side of side a can be considered as side b, the surface of the first press-formed member 11 on side b can be considered as S1b, and the surface of the second press-formed member 12 on side b can be considered as S2b. In Figure 3, for convenience, the upper side of the paper is considered as side a.

[0094] The symbols M1a, M1b, M2a, and M2b indicate the thickness of the aluminum-based plating layer. If no aluminum-based plating layer is present, its thickness is considered to be 0 mm. For example, if no aluminum-based plating layer 112 is present on the S1a surface, M1a is 0 mm. The thicknesses M1a and M2a of the aluminum-based plating layers 112 and 122 are values ​​measured outside the plating removal section 14, which will be described later.

[0095] The symbol Wa is the width of the weld bead 131 on side a. That is, the symbol Wa is the distance on side a between the toe 1311a of the weld bead 131 on the side of the first press-formed member and the toe 1312a of the weld bead 131 on the side of the second press-formed member. Wa for the butt joint is an estimated value of the total width of the aluminum-based plating layers 112, 122 on the S1a surface and the aluminum-based plating layers 112, 122 on the S2a surface that have fused into the weld bead 131. Wa÷2 for the butt joint is an estimated value of the width of the aluminum-based plating layer 112 on the S1a surface and the estimated width of the aluminum-based plating layer 122 on the S2a surface that have fused into the weld bead 131. Wa ÷ 2 × (M1a + M2a) is an estimated value of the total cross-sectional area of ​​the aluminum-based plating layers 112 and 122 on the S1a and S2a surfaces that have fused into the weld bead 131.

[0096] The symbol Wb is the width of the weld bead 131 on the b side. That is, the symbol Wb is the distance on the b side between the toe 1311b of the weld bead 131 on the first press-formed member side and the toe 1312b of the weld bead 131 on the second press-formed member side. Wb of the butt joint is an estimated value of the total width of the aluminum-based plating layer 112 on the S1b surface and the aluminum-based plating layer 122 on the S2b surface that have fused into the weld bead 131. Wb÷2 of the butt joint is an estimated value of the width of the aluminum-based plating layer 112 on the S1b surface and the aluminum-based plating layer 122 on the S2b surface that have fused into the weld bead 131. Wb÷2×(M1b+M2b) is an estimated value of the total cross-sectional area of ​​the aluminum-based plating layer 122 on the S1b surface and the S2b surface that have fused into the weld bead 131. In the above formula, (Wa÷2×(M1a+M2a)+Wb÷2×(M1b+M2b)) is an estimated value of the total cross-sectional area of ​​the aluminum-based plating layers 112 and 122 that have fused into the weld bead 131.

[0097] The coefficient "0.172" in the above formula is the value obtained by multiplying the specific gravity conversion value by 50%, and its technical significance is as described above in relation to lap fillet joints.

[0098] The welded joint 13 is a butt joint, and Al ＡＶＥIn a joint structure 1 that satisfies ≤0.172 × (Wa ÷ 2 × (M1a + M2a) + Wb ÷ 2 × (M1b + M2b)), the aluminum-based plating layers 112 and 122 are thicker outside the welded portion 13, while the average aluminum concentration of the weld bead 131 is reduced. This makes it possible to optimize the shape of the weld bead 131 while ensuring the scale prevention effect and corrosion resistance improvement effect of the aluminum-based plating layers 112 and 122. For example, as shown in Figure 11, a joint structure 1 that satisfies the above formula can be obtained by removing the aluminum-based plating layer at the position where the weld bead 131 will be placed before forming the weld bead 131.

[0099] The thickness of the aluminum-based plating layers 112 and 122 is measured by the following procedure. First, the welded portion 13 is cut perpendicular to the direction of extension of the weld bead 131 and embedded in resin. The embedded sample is polished. Line analysis of the cross-section of the sample is performed from the surface to the interior of the press-formed member using an electron beam microanalyzer (FE-EPMA). The elements to be analyzed in the line analysis are Fe and Al. The measurement conditions are an acceleration voltage of 15 kV, a beam diameter of approximately 100 nm, and an irradiation time of 1000 ms. The measurement pitch is a grid pattern with a pitch of 5 μm. Based on the line analysis results obtained, the interface between the surface layer and the intermetallic compound layer in the aluminum-based plating layer, and the interface between the intermetallic compound layer and the base steel member are identified. The "surface layer" refers to the part of the aluminum-based plating layer that is not alloyed with the base steel member. If the aluminum-based plating layer does not have an intermetallic compound layer, the entire aluminum-based plating layer corresponds to the surface layer.

[0100] In line analysis, regions where the aluminum concentration is determined to be 0.060 mass% or less are considered to be the base steel component, and regions where the aluminum concentration is determined to be greater than 0.060 mass% are considered to be the intermetallic compound layer or the surface layer. The sum of the thickness of the surface layer and the thickness of the intermetallic compound layer is considered to be the thickness of the aluminum-based plating layer.

[0101] (Plating removal portion 14) As shown in Figure 10, the joint structure 1 may have a plating removal portion 14 extending along the weld bead 131 between the weld bead 131 and the aluminum-based plating layers 112 and 122. The thickness of the aluminum plating layer in the plating removal portion 14 is smaller than that outside the plating removal portion 14.

[0102] The thickness of the aluminum plating layer in the plating removal section 14 may be 0 μm. If the plating thickness of the plating removal section 14 is 0 μm, the base steel members 111 and 121 will be exposed in the plating removal section 14. On the other hand, the thickness of the aluminum-based plating layer in the plating removal section 14 may be greater than 0% to 80% or less of the thickness of the aluminum-based plating layers 112 and 122 outside the plating removal section 14. In this case, the base steel members 111 and 121 will not be exposed in the plating removal section 14.

[0103] As described later, when manufacturing the joint structure 1 according to this embodiment, it is preferable to remove the aluminum-based plating layer before welding. This makes it possible to reduce the average aluminum concentration of the weld bead 131. The plating removal section 14 provided in the joint structure 1 is a trace of the process of removing the aluminum-based plating layer. By placing the weld bead 131 inside the plating removal section 14 and leaving the plating removal section 14 in the joint structure 1, the average aluminum concentration of the weld bead 131 can be further reduced.

[0104] On the other hand, the joint structure 1 does not necessarily have to have a plating removal portion 14. If the weld bead 131 is positioned so as to slightly exceed the outer edge of the plating removal portion 14, no plating removal portion 14 remains in the joint structure 1. In this case, the corrosion resistance around the weld bead 131 can be further improved.

[0105] The manufacturing method of the plating removal portion 14 is not particularly limited. For example, the aluminum-based plating layer of the press-formed product may be mechanically removed before welding. In this case, the plating removal portion 14 of the joint structure 1 will have machining marks. These machining marks are, for example, cutting marks or grinding marks. Alternatively, the aluminum-based plating layer of the press-formed product may be removed by laser ablation before welding. In this case, the plating removal portion 14 will have laser ablation marks. By observing the surface of the plating removal portion 14 under magnification with an optical microscope or electron microscope, machining marks or laser ablation marks can be easily confirmed.

[0106] Particularly preferably, in the plating removal portion 14, the base steel members 111 and 121 are exposed, and the plating removal portion 14 has machining marks. That is, it is preferable to remove the aluminum-based plating layer 112 and 122 over its entire thickness by machining, thereby forming machining marks on the base steel members 111 and 121.

[0107] The plating removal portion 14 can be formed on the surface of the aluminum-plated steel sheet before hot stamping. In this case, the plating removal process, such as machining and laser ablation, is performed on the aluminum-plated steel sheet. In this case, the plating removal portion 14 of the joint structure 1 will have heat treatment marks. These heat treatment marks are formed during hot stamping. In hot stamping, the aluminum-plated steel sheet is heated to the austenite temperature range. Therefore, the plating removal portion 14 formed before hot stamping will have traces of heat treatment, such as the adhesion of oxide scale.

[0108] On the other hand, the plating removal portion 14 can also be formed after hot stamping. In this case, the plating removal process, such as machining and laser ablation, is performed on the press-formed product having an aluminum-based plating layer. In this case, the plating removal portion 14 of the joint structure 1 does not have any heat treatment marks.

[0109] Heat treatment marks refer to traces and changes that remain on the surface and physical properties of metals and other materials after heat treatment. In principle, the presence or absence of heat treatment marks can be determined based on the surface shape of the plating removal area 14. Surface shape refers to, for example, the presence or absence of oxide scale, color tone, and luster. Specifically, if heat treatment marks are present, black or gray oxide scale is often attached to the surface of the plating removal area, and the luster is reduced. On the other hand, if there are no heat treatment marks, the plating removal area has a metallic luster. The presence or absence of heat treatment marks can also be determined based on the Vickers hardness of the plating removal area 14. The Vickers hardness of the plating removal area 14 with heat treatment marks tends to be higher than the Vickers hardness of the base steel member. On the other hand, the Vickers hardness of the plating removal area 14 without heat treatment marks is generally the same as the Vickers hardness of the base steel member.

[0110] (Thickness of press-formed members and chemical composition of base steel members 111, 121) The base steel member 111 of the first press-formed member 11 and the base steel member 121 of the second press-formed member 12 may be obtained by conventional methods including hot rolling, cold rolling, plating, etc., and are not particularly limited. The base steel members 111, 121 may be obtained by press-forming either hot-rolled steel sheets or cold-rolled steel sheets. The thickness of the base steel members 111, 121 may be set to a thickness appropriate for the purpose, and is not particularly limited. For example, the thickness of the flat portion of the base steel members 111, 121 is preferably 0.8 mm or more, or 1 mm or more. Also, the thickness of the flat portion of the base steel members 111, 121 is preferably 4 mm or less, or 3 mm or less. Note that the thickness of the press-formed members includes the thickness of the aluminum-based plating layers 112, 122.

[0111] The tensile strength of one or both of the base steel member 111 of the first press-formed member 11 and the base steel member 121 of the second press-formed member 12 is preferably in the range of 400 to 2700 MPa. More preferably, the tensile strength of one or both of the base steel member 111 of the first press-formed member 11 and the base steel member 121 of the second press-formed member 12 is 1500 MPa or more, or 1700 MPa or more. The tensile strength is measured in accordance with JIS Z 2241:2011 "Method for tensile testing of metallic materials". The tensile test specimen is taken from outside the weld 13.

[0112] The Vickers hardness of one or both of the base steel member 111 of the first press-formed member 11 and the base steel member 121 of the second press-formed member 12 is preferably in the range of 120 to 790 HV. More preferably, the Vickers hardness of one or both of the base steel member 111 of the first press-formed member 11 and the base steel member 121 of the second press-formed member 12 is 500 HV or higher, or 550 HV or higher. The Vickers hardness is measured in accordance with JIS Z 2244:2009 "Vickers hardness test - Test method". The test force in the Vickers hardness test is 9.8 N. The hardness test is performed on a cross section formed on the outside of the welded joint 13. The hardness test is performed at a depth of approximately 1 / 4 of the thickness of the base steel member from the surface of the base steel member in the said cross section.

[0113] The chemical composition of the base steel members 111 and 121 is not particularly limited, but for example, in mass%, C: 0.02% to 0.58%, Mn: 0.20% to 3.00%, Al: 0.005% to 0.060%, P: 0.03% or less, S: 0.010% or less, N: 0.010% or less, Ti: 0% to 0.20%, Nb: 0% to 0.20%, V: 0% to 1.0%, W: 0% to 1.0%, Cr Preferably, the chemical composition includes: 0% to 1.0% of ions, 0% to 1.0% of Mo, 0% to 1.0% of Cu, 0% to 1.0% of Ni, 0% to 1.0% of B, 0% to 0.0100%, 0% to 0.05% of Mg, 0% to 0.05% of Ca, 0% to 0.05% of REM, 0% to 0.05% of Sn, 0% to 0.5% of Bi, 0% to 0.05% of Si, and the remainder being Fe and impurities.

[0114] Either the first press-formed member 11 or the second press-formed member 12 does not need to have an aluminum-based plating layer. Naturally, the above-described configuration of the base steel members 111 and 121 may be applied to a press-formed member that does not have plating. If the press-formed member does not have an aluminum-based plating layer, the chemical composition of the press-formed member is considered to be the same as the chemical composition of the base steel member.

[0115] (Hardness of the weld bead 131 and heat-affected zone 132) In the joint structure 1, it is preferable that the average hardness of the weld bead 131 is greater than the minimum hardness of the heat-affected zone 132. This allows the weld bead 131 to plastically restrain the heat-affected zone 132, further increasing the joint strength of the joint structure 1.

[0116] The average hardness of the weld bead 131 shall be the average of the Vickers hardness measured at nine hardness measurement points in the reference cross-section of the weld bead 131. The reference cross-section is the cross-section of the weld bead 131 perpendicular to the weld line. The test force used when measuring the Vickers hardness of the weld bead 131 shall be 2.94 N (Newtons).

[0117] Since the shape of the weld bead 131 varies, the position of the hardness measurement points on the weld bead 131 is not strictly defined. It is sufficient to distribute nine hardness measurement points within the weld bead 131 and calculate the average hardness obtained from these measurement points. This generally suppresses the influence of hardness variations within the weld bead 131. For example, it is preferable to place the hardness measurement points in the center of the weld bead 131, near the surface of the weld bead 131, and near the melting boundary of the weld bead 131. The positions of the hardness measurement points on the weld bead 131 of lap fillet joints, T-joints, and butt joints are exemplified below.

[0118] If the welded joint 13 is an overlap fillet joint, the hardness of the weld bead 131 is preferably measured at the hardness measurement points P1 shown in Figure 1. The hardness measurement points P1 in Figure 1 are located at the following nine locations: (1) Near the toe 1311 on the first press-formed member side, near the toe 1312 on the second press-formed member side, and in the center of these locations, near the surface of the weld bead 131. (2) Near the molten boundary of the weld bead 131 on the second press-formed member side, near the root portion 1313, near the toe 1312 on the second press-formed member side, and in the center of these locations, near the molten boundary on the second press-formed member side of the weld bead 131. (3) Between (1) and (2) above, near the toe 1311 on the first press-formed member side, near the toe 1312 on the second press-formed member side, and in the center of these locations.

[0119] If the welded joint 13 is a T-joint, the hardness of the weld bead 131 is preferably measured at the hardness measurement point P1 shown in Figure 2. The hardness measurement point P1 in Figure 2 is located at the following nine locations: (1) Near the toe 1311 on the first press-formed member side, near the toe 1312 on the second press-formed member side, and in the center of these locations, near the surface of the weld bead 131 (2) Near the melting boundary of the root portion of the weld bead 131, near the toe 1311 on the first press-formed member side, near the toe 1312 on the second press-formed member side, and in the center of these locations (3) Between (1) and (2) above, near the toe 1311 on the first press-formed member side, near the toe 1312 on the second press-formed member side, and in the center of these locations

[0120] If the welded joint 13 is a butt joint, the hardness of the weld bead 131 is preferably measured at the hardness measurement points P1 shown in Figure 3. The hardness measurement points P1 in Figure 3 are located at the following nine locations: (1) Near the toe 1311 on the first press-formed member side, near the toe 1312 on the second press-formed member side, and in the center of these locations, on one surface of the weld bead 131 (2) Near the toe 1311 on the first press-formed member side, near the toe 1312 on the second press-formed member side, and in the center of these locations, on the other surface of the weld bead 131 (3) Between (1) and (2) above, near the toe 1311 on the first press-formed member side, near the toe 1312 on the second press-formed member side, and in the center of these locations

[0121] The minimum hardness of the heat-affected zone 132 is measured by the following procedure. The Vickers hardness of the first press-formed member 11 and the second press-formed member 12 are measured in a cross section perpendicular to the weld line. The hardness measurement is performed at a depth of 1 / 3 of the member's thickness from the surface of the member. The hardness measurement is performed continuously along the surface of the member, starting from the melting boundary of the weld bead and moving away from the weld bead. The center distance of the indentations for hardness measurement is 250 μm. Then, the minimum hardness value is selected for each of the first press-formed member 11 and the second press-formed member 12. From the first press-formed member 11 and the second press-formed member 12, the one with the smaller product of thickness and minimum hardness value is selected, and that minimum hardness value is considered to be the minimum hardness of the heat-affected zone 132. The test force when measuring Vickers hardness is 2.94 N (Newtons).

[0122] (2. Press-formed articles) Next, press-formed articles according to another embodiment of the present disclosure will be described. The press-formed article according to this embodiment has a base molded article and an aluminum-based plating layer 212 provided on one or both surfaces of the base molded article. Preferably, the press-formed article is used as the material for the following first press-formed members 11: (1) The first press-formed member 11 of the joining structure 1 according to this embodiment (see Figure 1), wherein the welded part 13 is an overlap fillet joint. (2) The first press-formed member 11 of the joining structure 1 according to this embodiment (see Figure 2), wherein the welded part 13 is a T-joint. (3) The first press-formed member 11 of the joining structure 1 according to this embodiment (see Figure 3), wherein the welded part 13 is a butt joint. Hereinafter, for the convenience of explanation, the press-formed article used as the material for the first press-formed member 11 will be referred to as the "first press-formed article 21". In the first press-formed product 21, a plating removal portion 24 is provided on the surface on which the aluminum-based plating layer 212 is applied, extending to the end of the first press-formed product 21.

[0123] As stated above, the first press-formed member 11 and the second press-formed member 12 constituting the butt joint are not distinguished in this disclosure. Therefore, naturally, the first press-formed product 21 can also be used as the material for the second press-formed member 12 of the joint structure 1 in which the welded portion 13 is a butt joint.

[0124] Alternatively, the press-formed product according to this embodiment has a base molded product and an aluminum-based plating layer 222 provided on one or both surfaces of the base molded product. Preferably, the press-formed product is used as the material for the following second press-formed members 12: (1) The second press-formed member 12 of the joining structure 1 according to this embodiment (see Figure 1), in which the welded portion 13 is an overlap fillet joint. (2) The second press-formed member 12 of the joining structure 1 according to this embodiment (see Figure 2), in which the welded portion 13 is a T-joint. (3) The second press-formed member 12 of the joining structure 1 according to this embodiment (see Figure 3), in which the welded portion 13 is a butt joint. Hereinafter, for the convenience of explanation, the press-formed product used as the material for the second press-formed member 12 will be referred to as the "second press-formed product 22". In the second press-formed product 22, a plating removal portion 24 is provided in the area of ​​the aluminum-based plating layer 222 that is to be welded.

[0125] Figure 11 shows an enlarged perspective view of an example of the first press-formed product 21 and the second press-formed product 22 according to this embodiment. Figure 11 shows the flange portion B of the hat-shaped member in Figure 4 just before fillet welding. The hat-shaped member on the upper side of the paper in Figure 11 is the first press-formed product 21 according to this embodiment. The plate-shaped member on the lower side of the paper in Figure 11 is the second press-formed product 22 according to this embodiment.

[0126] The first press-formed product 21, which is a hat-shaped member, is provided with an aluminum-based plating layer 212. Furthermore, a plating removal portion 24 extending to the end of the flange portion B is provided on the surface where the aluminum-based plating layer 212 is provided. Note that the plating removal portion 24 of the first press-formed product 21 does not need to be in complete contact with the end of the first press-formed product 21. A small portion of the aluminum-based plating layer 212 may remain at the tip of the plating removal portion 24 of the first press-formed product 21. In the first press-formed product 21, the distance between the plating removal portion 24 and the end can be, for example, 3 mm or less, 2 mm or less, or 1 mm or less.

[0127] The second press-formed product 22, which is a plate-shaped member, is also provided with an aluminum-based plating layer 222. Furthermore, a plating removal section 24 is provided in the area of ​​the aluminum-based plating layer 222 that is scheduled to be welded.

[0128] By fillet welding the flange portion B of the first press-formed product 21 and the second press-formed product 22 along the end of the flange portion B, the joint structure 1 illustrated in Figure 4 is obtained. During fillet welding, by forming the weld bead 131 inside the plating removal portion 24, a joint structure 1 having a plating removal portion 14, as illustrated in Figure 10, is obtained.

[0129] The shape of the plating removal portion 14 of the second press-formed product 22 can be varied depending on the shape of the second press-formed product 22, the shape of the first press-formed product 21 to be joined thereto, and the position where the weld bead 131 is placed. Specific examples of the second press-formed product 22 are shown in Figures 12, 13, and 14.

[0130] The plating removal portion 24 of the second press-formed product 22 in Figure 12 is formed along the edge of the second press-formed product 22. Furthermore, both longitudinal ends of the plating removal portion 24 are in contact with the edge of the second press-formed product 22 (i.e., both longitudinal ends of the flange of the hat-shaped member). However, it is preferable that the portion of the plating removal portion 24 other than the longitudinal ends is far removed from the edge of the second press-formed product 22.

[0131] The plating removal portion 24 of the second press-formed product 22 in Figure 13 extends in a direction perpendicular to the longitudinal direction of the hat-shaped member. The portions of the plating removal portion 24, excluding both ends in the longitudinal direction, are far removed from the ends of the second press-formed product 22. The second press-formed product 22 in Figure 13 can be suitably used as the material for the second press-formed member 12 of the joining structure 1 in Figure 5.

[0132] In the second press-formed product 22 illustrated in Figures 12 and 13, it is preferable that the distance between the portion of the plating removal section 24 excluding both ends in the longitudinal direction and the end of the second press-formed product 22 be, for example, 4 mm or more, 5 mm or more, or 10 mm or more. However, both ends in the longitudinal direction of the plating removal section 24 may be in contact with the end of the second press-formed product 22.

[0133] The plating removal portion 24 of the second press-formed product 22 in Figure 14 is provided on the top plate portion A of the hat-shaped member. The plating removal portion 24 in Figure 14 is provided along the longitudinal end of the hat-shaped member and along the bend between the top plate portion A and the side plate portion C. The plating removal portion 24 is located far from the end of the second press-formed product 22. The second press-formed product 22 in Figure 14 can be suitably used as the material for the second press-formed member 12 of the joining structure 1 in Figure 6.

[0134] In the second press-formed product 22 illustrated in Figure 14, it is preferable to set the distance between the plating removal portion 24 and the edge of the second press-formed product 22 to, for example, 4 mm or more, 5 mm or more, or 10 mm or more over the entire length of the plating removal portion 24.

[0135] (3. Aluminum-plated steel sheet) Next, an aluminum-plated steel sheet according to another embodiment of the present disclosure will be described. The aluminum-plated steel sheet according to this embodiment is an aluminum-plated steel sheet for manufacturing the first press-formed product 21 according to this embodiment described above, and comprises a base steel sheet and an aluminum-plated layer 312 provided on one or both surfaces of the base steel sheet, wherein a plating removal portion 34 extending to the end of the aluminum-plated steel sheet is provided on the surface on which the aluminum-plated layer 312 is provided. The first press-formed product 21 can be obtained by press-forming this aluminum-plated steel sheet. Hereinafter, the aluminum-plated steel sheet for manufacturing the first press-formed product 21 will be referred to as the "first aluminum-plated steel sheet 31".

[0136] Alternatively, the aluminum-plated steel sheet according to this embodiment is an aluminum-plated steel sheet for manufacturing the second press-formed product 22 according to this embodiment, having a base steel sheet and an aluminum-plated layer 322 provided on one or both surfaces of the base steel sheet, wherein a plating removal portion 34 is provided in the welding area of ​​the surface on which the aluminum-plated layer 322 is provided. The second press-formed product 22 can be obtained by press-forming this aluminum-plated steel sheet. Hereinafter, the aluminum-plated steel sheet for manufacturing the second press-formed product 22 will be referred to as the "second aluminum-plated steel sheet 32".

[0137] Figure 15 shows a perspective view of an example of the first aluminum-plated steel sheet 31. An aluminum-plated layer 312 is provided on the surface of the first aluminum-plated steel sheet 31 shown in Figure 15. On the surface where the aluminum-plated layer 312 is provided, a plating removal portion 34 is provided at the edge of the first aluminum-plated steel sheet 31. By press-forming the first aluminum-plated steel sheet 31 of Figure 15, the first press-formed product 21 shown on the upper side of Figure 11 can be obtained.

[0138] In the first aluminum-plated steel sheet 31, the plating removal portion 34 does not need to be in complete contact with the edge of the first aluminum-plated steel sheet 31. A slightly wide aluminum-plated layer 312 may be left at the tip of the plating removal portion 34 of the first aluminum-plated steel sheet 31. In the first aluminum-plated steel sheet 31, the distance between the plating removal portion 34 and the edge of the first aluminum-plated steel sheet 31 can be, for example, 3 mm or less, 2 mm or less, or 1 mm or less.

[0139] Figure 16 shows a perspective view of an example of a second aluminum-plated steel sheet 32. An aluminum-plated layer 322 is provided on the surface of the second aluminum-plated steel sheet 32 ​​in Figure 16. On the surface where the aluminum-plated layer 322 is provided, a plating removal portion 34 is provided in the area to be welded. The portion of the plating removal portion 34, excluding both ends in the longitudinal direction, is widely separated from the edge of the second aluminum-plated steel sheet 32. By press-forming the second aluminum-plated steel sheet 32 ​​in Figure 16, the second press-formed product 22 shown in Figure 12 can be obtained. In the second aluminum-plated steel sheet 32 ​​illustrated in Figure 16, it is preferable that the distance between the portion of the plating removal portion 34, excluding both ends in the longitudinal direction, and the edge of the second aluminum-plated steel sheet 32 ​​be, for example, 4 mm or more, 5 mm or more, or 10 mm or more.

[0140] Figure 17 shows a perspective view of another example of the second aluminum-plated steel sheet 32. An aluminum-plated layer 322 is provided on the surface of the second aluminum-plated steel sheet 32 ​​in Figure 17. On the surface where the aluminum-plated layer 322 is provided, a plating removal section 34 is provided in the area to be welded. The plating removal section 34 is provided along the outer edge of the second aluminum-plated steel sheet 32. The plating removal section 34 is spaced far apart from the edge of the second aluminum-plated steel sheet 32 ​​throughout its entirety. In the second aluminum-plated steel sheet 32 ​​illustrated in Figure 17, it is preferable that the distance between the plating removal section 34 and the edge of the second aluminum-plated steel sheet 32 ​​be, for example, 4 mm or more, 5 mm or more, or 10 mm or more throughout the entirety of the plating removal section 34.

[0141] 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.

[0142] Various joint structures were manufactured by welding two press-formed products having an aluminum-based plating layer. The welding method was either arc welding or laser welding. The shape of the welded joint of the joint structure was one of the following: T-joint, lap fillet joint, or butt joint.

[0143] One press-formed part had a tensile strength of 1800 MPa and a thickness of 1.8 mm. The other press-formed part had a tensile strength of 1300 MPa and a thickness of 1.4 mm. In lap fillet joints and T-joints, the thicker press-formed part was used as the top plate. Both press-formed parts had an aluminum-based plating layer on both surfaces. The thickness of the aluminum-based plating layer was 30 μm. In the manufacture of some joint structures, the aluminum-based plating layer was removed from the area to be welded before welding.

[0144] Arc welding was performed using MAG welding. The welding speed for MAG welding was 60 cm / min. Laser welding was performed using a fiber laser oscillator. The welding speed for laser welding was 5 m / min. Filler wire was supplied to the molten pool during laser welding. The type of bead obtained by welding, the type of joint, and whether or not the plating was removed before welding are described in Table 2.

[0145] The welded joints of the various joint structures obtained using the procedure described above were cut along a plane perpendicular to the weld line of the weld bead. Component analysis of the cross-sections was performed to determine the average aluminum concentration of the weld bead, which is listed in Table 3. The unit of the average aluminum concentration listed in Table 3 is mass percent.

[0146] Furthermore, cross-sectional observations were performed to determine the bead shape and the thickness of the aluminum plating layer. For lap fillet joints, the formula 0.172 × (W1a × M1a + W1b × M1b + W2a × M2a) ÷ A was calculated. For T-joints, the formula 0.172 × (W1a × M1a + W2a × M2a) ÷ A was calculated. For butt joints, the formula 0.172 × (Wa ÷ 2 × (M1a + M2a) + Wb ÷ 2 × (M1b + M2b)) was calculated. These values ​​are listed in the "Calculated Value" column of Table 3. The unit of the "Calculated Value" listed in Table 3 is mass %.

[0147] Furthermore, cross-sectional observations were conducted at five locations to evaluate the shape of the weld bead. The locations for cross-sectional observations were evenly distributed across the weld bead. The evaluation criteria were as follows: Joint structures evaluated as A or B were considered to have an optimized weld bead shape. The evaluation results are shown in Table 3. A: There is almost no indentation along the entire length of the weld bead. B: There is an indentation of 10% or less of the plate thickness along the entire length of the weld bead. C: Neither A nor B applies.

[0148] In the case of lap fillet joints, the depth of the weld bead recess was determined by the following two criteria: (1) The depth of the recess is measured with respect to the surface S1a of the upper plate, i.e., the first press-formed member. A recess is determined to exist if the surface of the weld bead is on the side of the second press-formed member beyond the imaginary line VL shown in Figure 1. The maximum distance between the surface of the weld bead and the imaginary line VL in the recess is the depth of the recess with respect to surface S1a. (2) The depth of the recess is measured with respect to the surface S2a of the lower plate, i.e., the second press-formed member. A recess is determined to exist if the surface of the weld bead is on the side of the second press-formed member beyond the imaginary line along the surface S2a of the second press-formed member in Figure 1. The maximum distance between the surface of the weld bead and the imaginary line along the surface S2a of the second press-formed member in the recess is the depth of the recess with respect to surface S2a. The dent was evaluated based on the larger of the two depths of the dents measured according to the criteria (1) and (2) above. Generally, the term "weld bead dent" can refer to both undercut and underfill in the weld bead. Undercut refers to the groove that occurs at the toe. Underfill refers to the dent that occurs near the center of the weld bead. In this embodiment as well, the term "weld bead dent" is used as a concept that includes both undercut and underfill.

[0149] In T-joints, the depth of the weld bead recess was determined by the following two criteria: (1) The depth of the recess is measured with respect to the upper plate, i.e., the surface S1a of the first press-formed member. A recess is determined to exist if the surface of the weld bead is on the side of the surface S1b of the first press-formed member, beyond the imaginary line along the surface S1a of the first press-formed member in Figure 2. The maximum distance between the surface of the weld bead and the imaginary line along surface S1a in the recess is the depth of the recess with respect to surface S1a. (2) The depth of the recess is measured with respect to the lower plate, i.e., the surface S2a of the second press-formed member. A recess is determined to exist if the surface of the weld bead is on the side of the surface S2b of the second press-formed member, beyond the imaginary line along the surface S2a of the second press-formed member in Figure 2. The maximum distance between the surface of the weld bead and the imaginary line along the surface S2a of the second press-formed member in the recess is the depth of the recess with respect to surface S2a. The dent was evaluated based on the greater of the two dent depths measured according to the criteria (1) and (2) above.

[0150] In butt joints, the depth of the weld bead recess was determined by the following procedure. The thicknesses of the two press-formed parts constituting the butt joint were 1.8 mm and 1.4 mm, as described above. The recess was evaluated at the toe of the thinner press-formed part, i.e., the press-formed part with a thickness of 1.4 mm. Two surfaces of the 1.4 mm press-formed part were used as a reference for measuring the depth of the recess. (1) The maximum distance between the upper surface of the weld bead and a virtual line along the upper surface of the 1.4 mm press-formed part, near the toe of the 1.4 mm press-formed part, is the depth of the upper recess. (2) The maximum distance between the lower surface of the weld bead and a virtual line along the lower surface of the 1.4 mm press-formed part, near the toe of the 1.4 mm press-formed part, is the depth of the lower recess. The indentation was evaluated based on the sum of (1) the upper indentation and (2) the lower indentation. For example, in an observation cross-section where the sum of the indentations exceeds 10% of the plate thickness, the indentation was evaluated as C. This evaluation was performed at five observation cross-sections to make a comprehensive judgment on the indentation of the weld bead.

[0151]

[0152]

[0153] In joint structures where the average aluminum concentration of the weld bead was 1.00% by mass or less, the shape of the weld bead was optimized.

[0154] 1 Joining structure 11 First press-formed member 111 Base steel member 112 Aluminum-based plating layer 12 Second press-formed member 121 Base steel member 122 Aluminum-based plating layer 13 Welded part 131 Weld bead 1311 Toe on the first press-formed member side 1312 Toe on the second press-formed member side 1313 Root part 132 Heat-affected zone 14 Plating removal part 21 First press-formed product 212 Aluminum-based plating layer 22 Second press-formed product 222 Aluminum-based plating layer 24 Plating removal part 31 First aluminum-based plated steel sheet 311 Base steel sheet 312 Aluminum-based plating layer 32 Second aluminum-based plated steel sheet 321 Base steel sheet 322 Aluminum-based plating layer 34 Plating removal part

Claims

1. A press-formed member and a second press-formed member made of steel; a weld bead joining the first press-formed member and the second press-formed member; and a heat-affected zone surrounding the weld bead, wherein one or both of the first press-formed member and the second press-formed member have an aluminum-based plating layer on at least one surface, and the average aluminum concentration of the weld bead is Al ＡＶＥ A bonding structure in which the amount is 1.0 mass% or less.

2. The joining structure according to claim 1, characterized in that the first press-formed member, the second press-formed member, and the weld bead form an overlap fillet joint, and the weld bead joins the end face of the first press-formed member and the surface of the second press-formed member.

3. When the surface of the first press-formed member opposite to the second press-formed member is defined as surface S1a, the surface of the first press-formed member on the side of the second press-formed member is defined as surface S1b, and the surface of the second press-formed member on the side of the first press-formed member is defined as surface S2a, the average aluminum concentration of the weld bead Al ＡＶＥ The joining structure according to claim 2, characterized in that M1a, M1b, M2a, W1a, W1b, W2a, and A, which are values ​​measured in a cross section perpendicular to the weld line of the weld bead, satisfy the following formula. ＡＶＥ ≤ 0.172 × (W1a × M1a + W1b × M1b + W2a × M2a) ÷ A where, M1a is the thickness in units mm of the aluminum-based plating layer on the S1a surface, M1b is the thickness in units mm of the aluminum-based plating layer on the S1b surface, M2a is the thickness in units mm of the aluminum-based plating layer on the S2a surface, W1a is the distance in units mm between the intersection X of the imaginary line along the S1a surface and the surface of the weld bead and the toe of the weld bead on the side of the first press-formed member, W1b is the distance in units mm between the intersection Y of the surface of the weld bead and the S1b surface, measured in a direction parallel to the imaginary line and the intersection X, W2a is the distance in units mm between the intersection Z of the surface of the weld bead and the S2a surface and the toe of the weld bead on the side of the second press-formed member. A is the unit of the weld bead in mm. ２ This is the cross-sectional area.

4. The joining structure according to claim 2 or 3, characterized in that the penetration depth of the weld bead in the second press-formed member is 50% or more of the thickness of the second press-formed member.

5. The joining structure according to claim 1, characterized in that the first press-formed member, the second press-formed member, and the weld bead form a T-joint, and the end face of the first press-formed member abuts against the surface of the second press-formed member.

6. When the surface of the first press-formed member on which the weld bead is located is defined as surface S1a, and the surface of the second press-formed member on the side of the first press-formed member is defined as surface S2a, the average aluminum concentration of the weld bead is Al ＡＶＥ The joining structure according to claim 5, characterized in that W1a, W2a, M1a, M2a, and A, which are values ​​measured in a cross section perpendicular to the weld line of the weld bead, satisfy the following formula. ＡＶＥ ≤ 0.172 × (W1a × M1a + W2a × M2a) ÷ A where, M1a is the thickness in units mm of the aluminum-based plating layer on the S1a surface, M2a is the thickness in units mm of the aluminum-based plating layer on the S2a surface, W1a is the distance in units mm of the weld bead between the toe end on the first press-formed member side and the S2a surface, measured in a direction parallel to the S1a surface, W2a is the distance in units mm of the weld bead between the toe end on the second press-formed member side and the intersection point of the weld bead and the S2a surface at the mating surface of the first press-formed member and the second press-formed member, measured along the S2a surface, and A is the thickness in units mm of the weld bead ２ This is the cross-sectional area.

7. The joining structure according to claim 1, characterized in that the first press-formed member, the second press-formed member, and the weld bead form a butt joint.

8. When the surface of the first press-forming member facing the a side, which is one side of the first press-forming member, is defined as the S1a surface, the surface of the second press-forming member facing the a side of the first press-forming member is defined as the S2a surface, the surface of the first press-forming member facing the b side, which is the other side of the first press-forming member, is defined as the S1b surface, and the surface of the second press-forming member facing the b side of the first press-forming member is defined as the S2b surface, the average aluminum concentration Al of the weld bead ＡＶＥ and Wa, Wb, M1a, M1b, M2a, M2b, and A, which are values measured in a cross-section perpendicular to the weld line of the weld bead, satisfy the following formula. The joining structure according to claim 7, characterized in that: Al ＡＶＥ ≦0.172×(Wa÷2×(M1a + M2a) + Wb÷2×(M1b + M2b))÷A Here, M1a is the thickness in mm per unit of the aluminum-based plating layer on the S1a surface, M1b is the thickness in mm per unit of the aluminum-based plating layer on the S1b surface, M2a is the thickness in mm per unit of the aluminum-based plating layer on the S2a surface, M2b is the thickness in mm per unit of the aluminum-based plating layer on the S2b surface, Wa is the width in mm per unit of the weld bead on the a side of the joining structure, Wb is the width in mm per unit of the weld bead on the b side of the joining structure, and A is the cross-sectional area in mm ２ per unit of the weld bead.

9. The joining structure according to any one of claims 1 to 8, characterized in that the joining structure has a plating removal portion extending along the weld bead between the weld bead and the aluminum-based plating layer.

10. The bonding structure according to claim 9, characterized in that the plated removal portion has machining marks or laser ablation marks.

11. The joining structure according to claim 9 or 10, characterized in that the base steel member is exposed in the plating removal portion, and the plating removal portion has machining marks.

12. The joining structure according to any one of claims 9 to 11, characterized in that the plated removal portion has heat treatment marks.

13. The joining structure according to any one of claims 9 to 11, characterized in that the plated removal portion does not have heat treatment marks.

14. The thickness of the first press-formed member and the second press-formed member is 0.8 to 4.0 mm, and the chemical composition of the base steel members of the first press-formed member and the second press-formed member is, in mass%, C: 0.02% to 0.58%, Mn: 0.20% to 3.00%, Al: 0.005% to 0.060%, P: 0.03% or less, S: 0.010% or less, N: 0.010% or less, Ti: 0% to 0.20%, Nb: 0% to 0.20%, V: 0% to 1.0%, W: 0% to 1.0%, Cr: 0%. A bonding structure according to any one of claims 1 to 13, characterized in that it comprises ~1.0%, Mo: 0% to 1.0%, Cu: 0% to 1.0%, Ni: 0% to 1.0%, B: 0% to 0.0100%, Mg: 0% to 0.05%, Ca: 0% to 0.05%, REM: 0% to 0.05%, Sn: 0% to 0.5%, Bi: 0% to 0.05%, Si: 0% to 2.00%, and the remainder: Fe and impurities.

15. The joint structure according to any one of claims 1 to 14, characterized in that the average hardness of the weld bead is greater than the minimum hardness of the heat-affected zone.

16. The joining structure according to any one of claims 1 to 15, characterized in that the average aluminum concentration of the weld bead is 0.17% by mass or more.

17. The joining structure according to any one of claims 1 to 16, characterized in that the weld bead is an arc weld bead.

18. A press-formed product for a first press-formed member of a joint structure according to any one of claims 1 to 17, wherein the press-formed product has an aluminum-based plating layer on one or both of its surfaces, and the aluminum-based plating layer is provided on the surface having the aluminum-based plating layer, the plating removal portion extending to the end of the press-formed product.

19. An aluminum-plated steel sheet for manufacturing a press-formed product according to claim 18, wherein the aluminum-plated steel sheet has an aluminum-plated layer on one or both of its surfaces, and the aluminum-plated layer is provided on the surface having the aluminum-plated layer, the aluminum-plated steel sheet having a plating removal portion that extends to the end of the aluminum-plated steel sheet.

20. A press-formed product for a second press-formed member of a joint structure according to any one of claims 1 to 17, wherein the press-formed product has an aluminum-based plating layer on one or both surfaces, and the plating removal portion is provided in the welding-planned portion of the surface on which the aluminum-based plating layer is provided.

21. An aluminum-plated steel sheet for manufacturing a press-formed product according to claim 20, wherein the aluminum-plated steel sheet has an aluminum-plated layer on one or both of its surfaces, and the aluminum-plated layer is provided on the surface where welding is planned, and a plating removal portion is provided on the surface where the aluminum-plated layer is provided.

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