Structural member

Abstract

A structural member (100) comprises a member main body (10) and reinforcing plates (20). The member main body (10) includes a pair of vertical walls (111, 112) and a bottom plate (12). The pair of vertical walls (111, 112) face one other. The bottom plate (12) connects the vertical walls (111, 112) to one other. The bottom plate (12) includes protruding portions (121). The protruding portions (121) extend from one of the vertical walls (111, 112) to the other. The reinforcing plates (20) extend from one of the vertical walls (111, 112) to the other, and cover the protruding portions (121). The reinforcing plates (20) are joined to the member main body (10).

Description

Structural members

[0001] The present disclosure relates to structural members for vehicles.

[0002] A vehicle such as an automobile includes a plurality of structural members, such as bumper reinforcements, pillars, side sills, crash boxes, battery boxes, and floors.

[0003] For example, Patent Document 1 discloses a vehicle floor. The floor of Patent Document 1 includes a main floor panel and a reinforcing patch. The reinforcing patch has greater ductility than the main floor panel. The reinforcing patch is disposed on the main floor panel and bonded to the main floor panel.

[0004] International Publication No. 2021 / 094405

[0005] When a vehicle collides, a collision load is input to structural members. To ensure crashworthiness, structural members such as a battery box or floor may be joined to other frame members, such as cross members. However, this increases the number of parts in the vehicle, potentially complicating the structure or manufacturing process. Therefore, it is desirable to maximize the crashworthiness of the structural members themselves.

[0006] An object of the present disclosure is to enable a structural member for a vehicle to exhibit good crash resistance performance.

[0007] A structural member for a vehicle according to the present disclosure comprises a member body and a reinforcing plate. The member body includes a pair of vertical walls and a bottom plate. The pair of vertical walls face each other. The bottom plate connects the vertical walls. The bottom plate includes a convex portion. The convex portion extends from one side of the vertical walls to the other. The reinforcing plate extends from one side of the vertical walls to the other and covers the convex portion. The reinforcing plate is joined to the member body.

[0008] According to the present disclosure, it is possible to make the structural member for a vehicle itself exhibit good crash resistance performance.

[0009] FIG. 1 is a perspective view of a structural member according to an embodiment. FIG. 2 is a cross-sectional view showing a portion of the structural member shown in FIG. 1. FIG. 3 is a partial cross-sectional view of a blank used to manufacture the structural member. FIG. 4 is a partial cross-sectional view of a structural member manufactured by hot stamping the blank shown in FIG. 3. FIG. 5 is a cross-sectional view showing a portion of a structural member according to a second embodiment. FIG. 6 is another cross-sectional view showing a portion of a structural member according to the second embodiment. FIG. 7 is a cross-sectional view showing a portion of a structural member according to a modified example of each embodiment. FIG. 8 is a diagram showing the deformation behavior of a structural member according to Example 6. FIG. 9 is a diagram showing the deformation behavior of a structural member according to Comparative Example 6.

[0010] A structural member for a vehicle according to an embodiment includes a member body and a reinforcing plate. The member body includes a pair of vertical walls and a bottom plate. The pair of vertical walls face each other. The bottom plate connects the vertical walls. The bottom plate includes a convex portion. The convex portion extends from one side of the vertical walls to the other side. The reinforcing plate extends from one side of the vertical walls to the other side and covers the convex portion. The reinforcing plate is joined to the member body (first configuration).

[0011] In the first configuration, a convex portion is provided on the bottom plate of the member body. The convex portion extends from one vertical wall to the other vertical wall of the member body. Therefore, when a vehicle collides and a collision load is input to the structural member, the collision load can be supported by the convex portion. Furthermore, in the first configuration, the convex portion is reinforced by being covered by a reinforcing plate. Because the reinforcing plate covers the convex portion from one vertical wall to the other vertical wall, the collision load is more easily supported by the convex portion. This allows the structural member itself to exhibit good collision resistance performance.

[0012] In the structural member according to the first configuration, the member body may be a tray for a battery box. In this case, the member body may further include flanges. The flanges are connected to each of the vertical walls on the side opposite the bottom plate. The flanges protrude outward from the member body (second configuration).

[0013] In the structural member according to the second configuration, it is preferable that the reinforcing plate further covers the flange (third configuration).

[0014] Typically, a battery box tray has a lid attached to a flange. The flange may deform downward due to gravity acting on the lid or vertical vibrations while the vehicle is in motion. In the third configuration, the reinforcing plate covers the flange of the component body in addition to the protrusion, thereby reinforcing the flange. This makes it easier to suppress deformation of the flange.

[0015] In the structural member according to the third configuration, the reinforcing plate may be joined to the outer surface of the member body (fourth configuration).

[0016] In the fourth configuration, the reinforcing plate is provided on the outer surface of the main body, so that there is no step on the top surface of the flange due to the reinforcing plate. Therefore, when the lid is attached to the main body serving as a tray for the battery box and joined to the flange, it is easier to ensure a seal between the main body and the lid.

[0017] In the structural member according to any one of the first to fourth configurations, the member body and the reinforcing plate may each be formed of a plated steel sheet. The plated steel sheet has, for example, a base steel sheet and an aluminum-based plating layer. The aluminum-based plating layer covers both surfaces of the base steel sheet. In this case, the thickness of the aluminum-based plating layer on the reinforcing plate may be smaller than the thickness of the aluminum-based plating layer on the member body (fifth configuration).

[0018] In the structural member according to the fifth configuration, the reinforcing plate may be joined to the inner surface of the member body (sixth configuration).

[0019] In the sixth configuration, a reinforcing plate with a relatively thin plating is disposed inside the member body. In this case, the reinforcing plate is less likely to be exposed to the outside air, and therefore the reinforcing plate is less likely to rust.

[0020] In a structural member having any of the first to sixth configurations, the member body and the reinforcing plate may each be formed from a steel plate. In this case, the value of coefficient A calculated using the chemical composition of the steel plate forming the member body by the following formula (1) may be greater than the value of coefficient A calculated using the chemical composition of the steel plate forming the reinforcing plate by the following formula (1) (seventh configuration): A = 1.48 x (2.7 x C + 0.4 x Si + Mn + 0.45 x Ni + 0.8 x Cr + 2 x Mo). ３．４２ (1) However, the element symbols in the above formula (1) are substituted with the contents (mass %) of the corresponding elements.

[0021] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each drawing, the same or equivalent components are designated by the same reference numerals, and the same description will not be repeated.

[0022] First Embodiment [Configuration of Structural Member] Fig. 1 is a perspective view of a structural member 100 according to this embodiment. The structural member 100 is used in a vehicle such as an automobile. The structural member 100 is, for example, a battery box or a floor. In this embodiment, an example in which the structural member 100 is a battery box will be described.

[0023] Referring to FIG. 1 , a structural member 100 includes a member body 10 and a reinforcing plate 20 .

[0024] The member body 10 is, for example, a tray for a battery box. In this case, the member body 10 has an overall concave shape so that it can accommodate battery cells. In the example of Fig. 1, the member body 10 has a bottomed rectangular tubular shape. Although not shown, the opening of the member body 10 may be closed by a lid.

[0025] The member body 10 includes a pair of vertical walls 111 and 112, a bottom plate 12, and a flange 13. In this embodiment, the member body 10 further includes vertical walls 141 and 142.

[0026] The vertical walls 111, 112 are arranged opposite each other. For example, when the structural member 100 is installed in a vehicle, the vertical walls 111, 112 are arranged opposite each other in the vehicle width direction (left-right direction). When the structural member 100 is installed in a vehicle, the vertical walls 111, 112 may be arranged opposite each other in the vehicle length direction (front-rear direction).

[0027] The vertical walls 111 and 112 are connected to each other by other vertical walls 141 and 142. Specifically, one end of the vertical walls 111 and 112 is connected to each other by the vertical wall 141. The other end of the vertical walls 111 and 112 is connected to each other by the vertical wall 142.

[0028] The bottom plate 12 connects the vertical walls 111 and 112 to each other. The bottom plate 12 also connects the vertical walls 141 and 142 to each other. A space for arranging battery cells is defined by the vertical walls 111, 112, 141, and 142 and the bottom plate 12. The vertical walls 111, 112, 141, and 142 may be provided substantially perpendicular to the bottom plate 12 or may be inclined relative to the bottom plate 12.

[0029] The bottom plate 12 includes at least one protrusion 121. The protrusion 121 has a shape that is convex on the inside or outside of the member body 10 compared to other portions of the bottom plate 12. In the example of FIG. 1 , the protrusion 121 has a shape that is convex on the inside of the member body 10. The protrusion 121 extends from one of the vertical walls 111, 112 to the other. That is, the protrusion 121 extends from the vertical wall 111 toward the vertical wall 112 and reaches both the vertical walls 111, 112. The protrusion 121 is formed integrally with other portions of the bottom plate 12 and the vertical walls 111, 112.

[0030] In this embodiment, the bottom plate 12 includes a plurality of protrusions 121. The bottom plate 12 may include three or more protrusions 121. These protrusions 121 are arranged at intervals. The protrusions 121 may be arranged at substantially equal intervals.

[0031] The flange 13 is connected to each of the vertical walls 111 and 112 on the side opposite the bottom plate 12. In this embodiment, the flange 13 is also connected to each of the vertical walls 141 and 142 on the side opposite the bottom plate 12. The flange 13 protrudes from the vertical walls 111, 112, 141, and 142 to the outside of the member body 10. The flange 13 is provided on the member body 10 so as to surround the vertical walls 111, 112, 141, and 142 in a plan view of the member body 10. When the member body 10 is a tray for a battery box, a lid (not shown) is joined to the flange 13. To ensure the sealing of the battery box, for example, a gasket, an O-ring, or a known sealant (not shown) may be used between the flange 13 and the lid. The sealant is, for example, a coating agent mainly composed of resin.

[0032] In this embodiment, a plurality of reinforcing plates 20 are provided corresponding to the plurality of protrusions 121. The reinforcing plates 20 correspond to the protrusions 121 and are arranged at intervals. Each of the reinforcing plates 20 extends from at least one of the vertical walls 111 and 112 to the other and covers the corresponding protrusion 121. Like each protrusion 121, each of the reinforcing plates 20 extends from the vertical wall 111 toward the vertical wall 112 and reaches both the vertical walls 111 and 112. Each of the reinforcing plates 20 covers the entire corresponding protrusion 121.

[0033] Each of the reinforcing plates 20 is joined to the member body 10. In this embodiment, the reinforcing plates 20 are joined to the inner surface of the member body 10. Although not particularly limited, the reinforcing plates 20 are joined to the member body 10 by, for example, spot welding. Each of the reinforcing plates 20 covers a corresponding protrusion 121 from the inside of the member body 10.

[0034] In this embodiment, each reinforcing plate 20 includes a first portion 21 and a second portion 22. The first portion 21 covers the protrusion 121 and is joined to the bottom plate 12. The first portion 21 extends from one vertical wall 111 to the other vertical wall 112. The second portion 22 is provided continuously with both end portions of the first portion 21 in the extending direction. The second portion 22 is bent with respect to the first portion 21 and is provided along one of the vertical walls 111, 112. The second portion 22 is joined to the vertical wall 111 or the vertical wall 112.

[0035] 2 is a cross-sectional view taken along line II-II in FIG. 1, showing a cross section (a cross section perpendicular to the extending direction) of the protrusion 121 provided on the bottom plate 12. Referring to FIG. 2, the protrusion 121 of the bottom plate 12 is hollow and has, for example, a substantially arc shape in cross section. However, the protrusion 121 of the bottom plate 12 may have another cross-sectional shape, such as a rectangular shape.

[0036] When the member body 10 is a tray for a battery box, it is preferable that the proportion of the area of ​​the convex portion 121 relative to the area of ​​the bottom plate 12 is small from the viewpoint of ensuring the mounting capacity of the battery. The width L1 of the convex portion 121 is, for example, 90 mm or less, preferably 70 mm or less, and more preferably 50 mm or less. The width L1 of the convex portion 121 may be 30 mm or more. The width L1 of the convex portion 121 is the maximum length of the convex portion 121 in the width direction, when the direction perpendicular to the extension direction and height direction is defined as the width direction. The convex portion 121 may have a substantially constant width L1 over the entire length in the extension direction, or may have a width L1 that varies along the extension direction.

[0037] The height of the protrusion 121 is equal to or less than the height of the vertical walls 111, 112 ( FIG. 1 ). In this embodiment, the height of the protrusion 121 is smaller than the height of the vertical walls 111, 112. That is, the protrusion 121 does not reach the edge of the vertical walls 111, 112 on the flange 13 ( FIG. 1 ) side. The protrusion 121 may have a substantially constant height over the entire length in its extension direction, or may have a height that varies along the extension direction.

[0038] The first portion 21 of the reinforcing plate 20 covers at least the convex portion 121. The first portion 21 may further cover a portion of the bottom plate 12 adjacent to the convex portion 121. In the example of FIG. 2 , the first portion 21 includes a convex portion 211 and a flat portion 212. The convex portion 211 has a shape corresponding to the convex portion 121 of the bottom plate 12 and is disposed on the convex portion 121. The convex portion 211 may be in contact with the entire convex portion 121 of the bottom plate 12. The flat portion 212 is provided continuously on both sides of the convex portion 211. From the viewpoint of formability of the component body 10 and the reinforcing plate 20, the width L2 of the flat portion 212 is, for example, 10 mm or more. The width L2 of the flat portion 212 may be 40 mm or less. The width L2 of the flat portion 212 is the maximum length of the flat portion 212 in the width direction of the convex portion 121 of the bottom plate 12. The width L2 of the flat portion 212 may be substantially constant along the extension direction of the convex portion 121 of the bottom plate 12, or may vary.

[0039] The component body 10 and the reinforcing plate 20 may each be formed of a steel plate to ensure their strength. The component body 10 and the reinforcing plate 20 may each be formed of a plated steel plate, for example. Specifically, the component body 10 and the reinforcing plate 20 may each be formed of an aluminum-based plated steel plate.

[0040] The thickness of the component body 10 and the reinforcing plate 20 is, for example, 0.4 mm to 2.0 mm, and preferably 1.0 mm to 1.8 mm. The thickness of the reinforcing plate 20 is preferably greater than the thickness of the component body 10. However, the thickness of the reinforcing plate 20 may be equal to or less than the thickness of the component body 10.

[0041] The component body 10 and the reinforcing plate 20 may have a tensile strength of, for example, 980 MPa or more and 2200 MPa or less. The tensile strength of the reinforcing plate 20 may be the same as or different from the tensile strength of the component body 10.

[0042] The structural member 100 is manufactured by pressing a blank. The structural member 100 can be manufactured by hot stamping. For example, the blank 30 shown in FIG. 3 is pressed at an austenite transformation completion temperature (A ｃ３After heating to a temperature above the predetermined temperature (point), the heated blank 30 is formed into the structural member 100 using a die and then quenched, thereby manufacturing the structural member 100.

[0043] FIG. 3 is a partial cross-sectional view of the blank 30. As shown in FIG. 3, the blank 30 includes a steel plate 31 and a steel plate 32. The steel plate 31 is a steel plate for forming the member main body 10 (FIGS. 1 and 2). The steel plate 32 is a steel plate for forming the reinforcing plate 20 (FIGS. 1 and 2). In the blank 30, the steel plate 32 is overlapped and joined to the steel plate 31. The steel plate 32 is joined to the steel plate 31 by, for example, spot welding. The thickness of each of the steel plates 31 and 32 is, for example, 0.4 mm or more and 2.0 mm or less, and preferably 1.0 mm or more and 1.8 mm or less. The thickness of the steel plate 32 is preferably greater than the thickness of the steel plate 31. However, the thickness of the steel plate 32 may be equal to or less than the thickness of the steel plate 31.

[0044] The steel sheets 31, 32 are, for example, aluminum-based plated steel sheets. The steel sheet 31 has a base steel sheet 31a and an aluminum-based plated layer 31b. The aluminum-based plated layer 31b covers both surfaces of the base steel sheet 31a. The steel sheet 32 ​​has a base steel sheet 32a and an aluminum-based plated layer 32b. The aluminum-based plated layer 32b covers both surfaces of the base steel sheet 32a.

[0045] The chemical composition of the aluminum-based plating layers 31b, 32b is not particularly limited. Known aluminum-based plating layers (plating layers containing aluminum as the main component) can be used as the aluminum-based plating layers 31b, 32b. Although not particularly limited, the aluminum-based plating layers 31b, 32b are, for example, Al-Si-based plating layers. The aluminum-based plating layer 31b of the steel plate 31 may be the same as or different from the aluminum-based plating layer 32b of the steel plate 32. Similarly, the type of the base steel plates 31a, 32a is not particularly limited. The base steel plate 31a may be the same as or different from the base steel plate 32a.

[0046] In this embodiment, the coating weight W2 (g / m ２) is the coating weight W1 (g / m) of the aluminum-based plating layer 31b on the steel sheet 31. ２ ) The coating weight W1 of the aluminum-based plating layer 31b on the steel sheet 31 is the average coating weight on both surfaces of the base steel sheet 31a. Similarly, the coating weight W2 of the aluminum-based plating layer 32b on the steel sheet 32 ​​is the average coating weight on both surfaces of the base steel sheet 32a. The coating weights W1 and W2 are each 20 g / m ２ 120g / m or more ２ The deposition amounts W1 and W2 are preferably 30 g / m or less. ２ More preferably, 35 g / m ２ The deposition amounts W1 and W2 are preferably 115 g / m ２ More preferably, it is 100 g / m or less. ２ The difference between the adhesion amounts W1 and W2: W1-W2 is, for example, 10 (g / m ２ ) or more. W1-W2 is preferably 20 (g / m ２ ) or more, more preferably 30 (g / m ２ ) or more. W1-W2 is 80 (g / m ２ ) or less. W1-W2 is preferably 70 (g / m ２ ) or less, more preferably 60 (g / m ２ ) or less. The adhesion amounts W1 and W2 satisfy the relationship W1 / W2>1.0. W1 / W2 is preferably 1.2 or more, and more preferably 1.5 or more.

[0047] The method for forming the aluminum-based plating layer on the base steel sheet is not particularly limited, but may be, for example, a general hot-dip galvanizing method. That is, by immersing the base steel sheet 31a in a hot-dip aluminum plating bath and gas wiping with nitrogen, air, or the like, a plated steel sheet 31 having an adjusted coating weight W1 of the aluminum-based plating layer 31b can be obtained. Similarly, by immersing the base steel sheet 32a in a hot-dip aluminum plating bath and gas wiping with nitrogen, air, or the like, a plated steel sheet 32 ​​having an adjusted coating weight W2 of the aluminum-based plating layer 32b can be obtained. When the aluminum-based plating layer is formed by the hot-dip galvanizing method, an Al-Fe-based alloy layer is formed at the interface between the base steel sheet and the aluminum-based plating layer due to the elution of Fe during the hot-dip galvanizing process.

[0048] In the example shown in Fig. 3, a coating 32c is provided on a steel plate 32. Of both surfaces of the steel plate 32, the surface opposite to the steel plate 31 is covered with the coating 32c. On the other hand, the steel plate 31 is not provided with the coating 32c. The coating 32c is a substantially black coating. For example, the lightness L ＊ Value (CIE 1976 lightness index L defined in JIS Z8781-4:2013) ＊ ) is 60 or less, the coating 32c can be determined to be substantially black. The coating 32c may be a carbon-based surface treatment coating (a coating containing carbon (C)). For example, the surface treatment coating described in WO 2022 / 215229 can be used as the coating 32c.

[0049] FIG. 4 is a partial cross-sectional view of a structural member 100 manufactured by hot stamping a blank 30. Referring to FIG. 4, a convex portion 121 is formed on the steel sheet 31 (FIG. 3) by hot stamping, and a convex portion 211 is formed on the steel sheet 32 ​​(FIG. 3). In the structural member 100 after hot stamping, the member body 10 is still a plated steel sheet having a base steel sheet 31a and an aluminum-based plating layer 31b. The reinforcing plate 20 is also a plated steel sheet having a base steel sheet 32a and an aluminum-based plating layer 32b. However, compared to the state of the blank 30 (FIG. 3), the aluminum-based plating layers 31b, 32b in the structural member 100 have been alloyed with iron more extensively due to heating during hot stamping. The reinforcing plate 20 may further have a coating 32c. The composition of the coating 32c on the reinforcing plate 20 may change through hot stamping.

[0050] In this embodiment, the thickness of the aluminum-based plating layer 32b on the reinforcing plate 20 is smaller than the thickness of the aluminum-based plating layer 31b on the member body 10. When the average thickness (plating thickness) of the aluminum-based plating layer 31b on both surfaces of the steel sheet 31 is K1 (μm), and the average thickness (plating thickness) of the aluminum-based plating layer 31b on both surfaces of the steel sheet 32 ​​is K2 (μm), the plating thickness K2 of the steel sheet 32 ​​is smaller than the plating thickness K1 of the steel sheet 31. The difference between the plating thicknesses K1 and K2, K1 - K2, is, for example, 7 μm or more. K1 - K2 may be 33 μm or less. Furthermore, the plating thicknesses K1 and K2 may satisfy the relationship K1 / K2 > 1.0. K1 / K2 is preferably 1.2 or more, more preferably 1.5 or more.

[0051] The thickness of the aluminum-based plating layer 31b on the component body 10 and the thickness of the aluminum-based plating layer 32b on the reinforcing plate 20 can be measured as follows. Specifically, a vehicle is dismantled to obtain a structural member 100, and an analytical sample is obtained from the structural member 100, for example, by laser cutting. For example, analytical samples are obtained from each of the component body 10 and the reinforcing plate 20 of the structural member 100. For each analytical sample obtained from the component body 10 and the reinforcing plate 20, cross sections of the aluminum-based plating layer are subjected to nital etching and then observed with an optical microscope (area: 100 μm × 100 μm). The thickness of the plating layer is measured in three fields of view, and the average value of the thicknesses of the plating layer measured in the three fields of view can be used as the plating thickness. In many cases, an electrodeposition coating film or the like is present on the outermost surface of the structural member 100. In such cases, the plating layer present below the electrodeposition coating film and above the base steel sheet is observed.

[0052] In this embodiment, steel plates 31, 32 (FIG. 3) are integrated by welding before hot stamping. A structural member 100 including a member body 10 and a reinforcing plate 20 is formed as a single part from a blank 30 (FIG. 3) including the steel plates 31, 32. In this case, even if softening of the heat-affected zone (HAZ softening) occurs during welding before forming, the HAZ softening is reduced by the heat treatment of hot stamping, and the hardness difference between the heat-affected zone and the non-welded zone in the resulting structural member 100 is reduced. Therefore, in at least one reinforcing plate 20 of the structural member 100 shown in FIG. 1, the minimum Vickers hardness of the heat-affected zone of the weld is set to HV ｗｅｌｄ , when the Vickers hardness of the non-welded part is HV, HV-HV ｗｅｌｄ is, for example, 30% or less of HV.

[0053] The Vickers hardness of the heat-affected zone and non-welded zone of the reinforcing plate 20 can be measured by a Vickers hardness test specified in JIS Z 2244-1:2020. That is, first, a test specimen including the component body 10, the reinforcing plate 20, and the welded zone is obtained by laser cutting or the like at a position passing through the weld center of the welded zone of the structural member 100. The test specimen is then embedded in resin so that a cross section passing through the component body 10, the reinforcing plate 20, and the welded zone's weld center is located on the surface, and the cross section is polished. Next, Vickers hardness is measured in accordance with JIS Z 2244-1:2020, for example, at a test force of 0.49 N and a measurement interval (pitch) of 0.1 to 0.2 mm, from the surface of the welded zone of the reinforcing plate 20 at a position 1 / 4 of the plate thickness from the welded zone's welded center side to a position 12.0 mm outward from the welded center. The minimum value of the measured Vickers hardness is the minimum Vickers hardness of the heat-affected zone of the reinforcing plate 20. Furthermore, the Vickers hardness is measured in accordance with JIS Z 2244-1:2020 at a position 15.0 mm or more away from the weld center of the welded portion and at a position 1 / 4 of the way in the plate thickness direction from the surface of the weld center side of the welded portion of the reinforcing plate 20, using a test force of, for example, 0.49 N. This Vickers hardness is defined as the Vickers hardness of the non-welded portion of the reinforcing plate 20.

[0054] [Effect] In the structural member 100 according to this embodiment, a convex portion 121 is provided on the bottom plate 12 of the member body 10. The convex portion 121 extends from one of the vertical walls 111, 112 to the other in the member body 10. Therefore, when a vehicle collides and a collision load is input to the structural member 100, the collision load can be supported by the convex portion 121. Furthermore, in the structural member 100, the reinforcing plate 20 covers the convex portion 121, thereby reinforcing the convex portion 121. Because the reinforcing plate 20 extends from at least one of the vertical walls 111, 112 to the other and covers the convex portion 121, the collision load can be more easily supported by the convex portion 121. This provides the structural member 100 with collision resistance, allowing the structural member 100 itself to exhibit excellent collision resistance.

[0055] In this embodiment, the member body 10 is a tray for a battery box. The member body 10 includes a flange 13 that protrudes outward from the member body 10 from the vertical walls 111, 112, 141, and 142. When a lid is attached to the member body 10, the lid is joined to the flange 13, thereby sealing the member body 10 and making it easier to ensure sealing between the member body 10 and the lid.

[0056] In this embodiment, the structural member 100 is manufactured by hot stamping a blank 30. The portion of the steel sheet 31 corresponding to the member main body 10 where the steel sheet 32 ​​serving as the reinforcing plate 20 is joined is thicker and has a larger heat capacity than the other portions, and therefore is less likely to rise in temperature when heated during hot stamping. However, in this embodiment, the coating weight W2 (thickness) of the aluminum-based plating layer 32b on the steel sheet 32 ​​is smaller than the coating weight W1 (thickness) of the aluminum-based plating layer 31b on the steel sheet 31. In this case, when the blank 30 is heated during hot stamping, alloying of the aluminum-based plating layer 32b with iron progresses more quickly on the steel sheet 32 ​​than on the steel sheet 31, and the surface of the steel sheet 32 ​​changes from silver-white to black or a color close to silver-white. This increases the emissivity of the steel sheet 32, thereby increasing the temperature rise rate at the portion of the blank 30 where the steel sheet 32 ​​overlaps the steel sheet 31, and shortening the heating time for hot stamping. This improves the productivity of the structural member 100. Furthermore, by shortening the heating time of the blank 30, energy consumption in the heating process is reduced, and the cost and amount of greenhouse gases generated in the production of the structural member 100 can be reduced.

[0057] In this embodiment, the thickness of the aluminum-based plating layer 31b in the component body 10 is greater than the thickness of the aluminum-based plating layer 32b in the reinforcing plate 20. This ensures the rust prevention performance of the component body 10. Furthermore, in this embodiment, the reinforcing plate 20, in which the aluminum-based plating layer 32b is relatively thin, is provided on the inside of the component body 10. In this case, the reinforcing plate 20 is less likely to be exposed to the outside air, making the reinforcing plate 20 less likely to rust or the like.

[0058] In this embodiment, since the substantially black coating 32c is applied to the surface of the steel sheet 32, it is possible to increase the emissivity of the surface of the steel sheet 32. By increasing the emissivity of the surface of the steel sheet 32 ​​in advance, when the blank 30 is heated during hot stamping, it is possible to more quickly increase the temperature of the portion of the blank 30 where the steel sheet 32 ​​overlaps the steel sheet 31.

[0059] In the structural member 100 according to this embodiment, the height of the vertical walls 111, 112, 141, and 142 is greater than the height of the protrusion 121. In other words, the depth of the member body 10 is ensured to be greater than the height of the protrusion 121 provided on the bottom plate 12. In this case, the battery mounting capacity of the member body 10 is increased, and the degree of freedom in designing the storage section of the member body 10 can be increased.

[0060] 5 is a cross-sectional view of a structural member 100A according to a second embodiment taken at the position of a protrusion 121. The structural member 100A according to this embodiment differs from the structural member 100 according to the first embodiment in the arrangement of the reinforcing plate 20.

[0061] 5 , in a structural member 100A according to this embodiment, the reinforcing plate 20 is joined to the outer surface of the member body 10. The reinforcing plate 20 covers the convex portion 121 of the bottom plate 12 from the outside of the member body 10. More specifically, the convex portion 121 is covered from the outside of the bottom plate 12 by the first portion 21 of the reinforcing plate 20. The first portion 21 of the reinforcing plate 20 can include a convex portion 211 and a flat portion 212, similar to the first embodiment.

[0062] FIG. 6 is a view (longitudinal cross-sectional view) of the structural member 100A according to this embodiment, cut perpendicular to the width direction of the protruding portion 121. Referring to FIG. 6, the reinforcing plate 20 covers not only the protruding portion 121 of the bottom plate 12 but also the vertical wall 111 or 112 ( FIG. 1 ) and the flange 13 from the outside of the member body 10. More specifically, the reinforcing plate 20 further includes a third portion 23. The third portion 23 is continuous with the second portion 22 on the opposite side of the first portion 21. The third portion 23 is joined to the flange 13 by, for example, spot welding. In the example shown in FIG. 6, the third portion 23 may extend from the second portion 22 to the free end of the flange 13 in the longitudinal cross-sectional view.

[0063] When the component body 10 is a tray for a battery box, when a lid is joined to the flange 13, the flange 13 may be deformed downward due to gravity acting on the lid or vibrations in the vertical direction when the vehicle is traveling. In the example of this embodiment, the third portion 23 of the reinforcing plate 20 covers the flange 13, so the flange 13 can be reinforced by the reinforcing plate 20. This makes it easier to suppress deformation of the flange 13. Furthermore, in the example of this embodiment, the reinforcing plate 20 is provided on the outer surface of the component body 10, so no step caused by the reinforcing plate 20 is created on the upper surface of the flange 13. Therefore, when the lid is joined to the flange 13, it is easier to ensure sealing between the component body 10 and the lid.

[0064] Third Embodiment In the first embodiment described above, an example was described in which the adhesion amount (thickness) of the aluminum-based plating layer 32b of the steel plate 32 corresponding to the reinforcing plate 20 is reduced compared to the steel plate 31 corresponding to the member body 10. In the present embodiment, an example will be described in which the steel plate 31 is made of a highly hardenable material instead of or in addition to this.

[0065] 3 and 4 again, in the blank 30 and the structural member 100 formed therefrom, the steel plate 31 forming the member body 10 has a thinner wall in a portion where the steel plate 32 forming the reinforcing plate 20 is not overlapped compared to the portion where the steel plate 32 is overlapped. The chemical composition of the steel plate 31 may be different from the chemical composition of the steel plate 32. More specifically, the value of coefficient A calculated by the following formula (1) using the chemical composition of the steel plate 31 may be different from the value of coefficient A calculated by the formula (1) using the chemical composition of the steel plate 32. A = 1.48 x (2.7 x C + 0.4 x Si + Mn + 0.45 x Ni + 0.8 x Cr + 2 x Mo) ３．４２ (1)

[0066] The meaning of the coefficient A calculated by the formula (1) will be explained below. For example, as described in "Ueno Masakatsu and Ito Kametaro, 'A new prediction formula for hardenability of steel to replace the GROSSMANN formula,' Iron and Steel, The Iron and Steel Institute of Japan, 74th year (1988) No. 6, pp. 1073-1080," the critical cooling rate V has been used as an index of hardenability of steel materials. ｃ９０The critical cooling rate V ｃ９０ is the critical cooling rate (°C / s) at which a martensite structure of 90% or more in volume fraction is obtained, and logV ｃ９０ = 2.94 - 0.75β. β is calculated as 2.7 × C + 0.4 × Si + Mn + 0.45 × Ni + 0.8 × Cr + 2 × Mo. β represents the influence of each element on hardenability based on the amount of Mn. The larger β is, the higher the critical cooling rate V ｃ９０ becomes smaller, and the hardenability of the steel material becomes good.

[0067] There is a correlation between β, which indicates the influence of each element on hardenability, and the time from the completion of heating of the steel material until the start of diffusion transformation (transformation start time). The inventors performed tests on multiple hot stamping steel materials and regression analysis using the test results, and used the formula: A = 1.48 × β to convert β into the transformation start time. ３．４２ was constructed. A calculated by this formula is a coefficient (index value) that differs for each steel material depending on its chemical composition. Coefficient A corresponds to the transformation start time when only the influence of elements is considered, and a larger coefficient A indicates a steel material with better hardenability. Coefficient A roughly corresponds to the transformation start time when the steel plate thickness is 1.2 mm.

[0068] The element symbols in formula (1) are substituted with the content (mass%) of the corresponding element. That is, the coefficient A of the steel sheet 31 is calculated by substituting the content (mass%) of each element in the chemical composition of the steel sheet 31 into the corresponding element symbol in formula (1). When the steel sheet 31 is a plated steel sheet, the coefficient A of the steel sheet 31 is calculated by substituting the content (mass%) of each element in the chemical composition of the base steel sheet 31a into formula (1). Similarly, the coefficient A of the steel sheet 32 ​​is calculated by substituting the content (mass%) of each element in the chemical composition of the steel sheet 32 ​​into the corresponding element symbol in formula (1). When the steel sheet 32 ​​is a plated steel sheet, the coefficient A of the steel sheet 32 ​​is calculated by substituting the content (mass%) of each element in the chemical composition of the base steel sheet 32a into formula (1). The chemical compositions of the steel sheets 31, 32 do not change before and after hot stamping.

[0069] In the blank 30 and the structural member 100 formed therefrom, the value of the coefficient A calculated by the formula (1) using the chemical composition of the steel plate 31 is preferably larger than the coefficient A calculated by the formula (1) using the chemical composition of the steel plate 32. １ , the coefficient A of the steel plate 32 is A ２ When this is done, A １ -A ２ is preferably 0.10 or more, and more preferably 0.20 or more. １ -A ２ may be, for example, 11.50 or less.

[0070] The steel sheets 31 and 32 may have a chemical composition known as a steel sheet for hot stamping. For example, the chemical composition of the steel sheets 31 and 32 contains, in mass %, 0.05 to 0.50% C, 0.020 to 1.000% Si, 0.20 to 2.50% Mn, 0 to 0.50% Ni, 0 to 0.50% Cr, 0 to 0.5% Mo, and 0.0005 to 0.0050% B. The chemical composition of each of the steel plates 31, 32 may further contain, in mass %, one or more elements selected from the group consisting of Cu: 0.005 to 3.000%, Co: 0.005 to 0.500%, Sn: 0.005 to 0.500%, Ca: 0.0005 to 0.0050%, Mg: 0.0005 to 0.0050%, REM: 0.0005 to 0.0050%, and Sb: 0.0005 to 0.0200%.

[0071] The chemical compositions of the steel plates 31, 32 included in the blank 30 may be measured by a common analytical method. For example, analytical test pieces may be taken from each of the steel plates 31, 32 and measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry), thereby obtaining the chemical compositions of the steel plates 31, 32. In each analytical test piece, C may be measured using a combustion-infrared absorption method. The chemical compositions of the steel plates 31, 32 in the structural member 100 after hot stamping may be obtained by the same analytical method as for the blank 30.

[0072] When the hardenability of the steel plate 31 corresponding to the member body 10 and the steel plate 32 corresponding to the reinforcing plate 20 is the same, after the heating of the blank 30 for hot stamping is completed, the thin portion of the steel plate 31 where the steel plate 32 is not overlapped starts a phase transformation (diffusion transformation) from austenite to ferrite relatively quickly. However, in this embodiment, the coefficient A calculated based on the chemical composition of the steel plate 31 １ is the coefficient A calculated for the steel plate 32 based on its chemical composition. ２ is larger than . That is, the steel plate 31 forming the member body 10 is made of a material with higher hardenability than the steel plate 32 forming the reinforcing plate 20, in other words, a material that starts diffusion transformation slowly during cooling. Therefore, after heating of the blank 30 is completed, it is possible to delay the start of diffusion transformation in the thin-walled portion of the steel plate 31 where the steel plate 32 is not overlapped. As a result, when the blank 30 is hot stamped, the thin-walled portion can also be well hardened, making it easier to uniformize the hardness of the structural member 100.

[0073] The configuration of the steel plates 31, 32 in this embodiment can also be applied to the structural member 100A according to the second embodiment.

[0074] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure.

[0075] In the above embodiments, one example of the shape of the member body 10 is presented, but the shape of the member body 10 is not limited to the examples in the above embodiments. For example, in the examples of the above embodiments, the height of the vertical walls 111, 112, 141, and 142 is greater than the height of the protrusion 121. However, as shown in FIG. 7 , the height of the protrusion 121 may be substantially the same as the height of the vertical walls 111 and 112.

[0076] In the above embodiments, the structural members 100, 100A are described as battery boxes. However, the structural members 100, 100A are not limited to this and may be, for example, a vehicle floor. That is, the structural member body 10 may be a floor panel. In this case, the structural member body 10 includes at least a pair of vertical walls 111, 112 and a bottom plate 12. The structural member body 10 may further include a flange 13 continuous with the vertical walls 111, 112. The structural member body 10 may not include the vertical walls 141, 142.

[0077] The present disclosure will be described in more detail below with reference to examples, although the present disclosure is not limited to the following examples.

[0078] First Example In order to confirm the effects of the present disclosure, CAE analysis was performed using commercially available software (AUTOFORM R.10, manufactured by AUTOFORM) while changing the type and thickness of steel plates forming structural members for vehicles.

[0079]

[0080] The types of steel sheets (material types) used in this analysis are shown in Table 1. Table 1 shows, for each material, the content (mass%) of each element in the base material and the coefficient A calculated by the above-mentioned formula (1).

[0081] The analysis conditions and results of this example are shown in Table 2. In Table 2, material (1) forms the main body of the structural member, and material (2) forms the reinforcing plate of the structural member. The plate thickness of material (1) is 1.0 mm, and the plate thickness of material (2) is 1.2 mm.

[0082]

[0083] In Table 2, "time to reach 910°C" means the time from the start of heating the blank until the material (1) reaches 910°C (A ｃ３The "heating completion time" is the time required for the portion of the blank that rises the temperature the slowest to reach 910°C from the start of heating the blank until it becomes hot stampable. The "process window (PW)" is the value obtained by subtracting the heating completion time from the time obtained by adding the allowable heating time (250 seconds) after the material (1) reaches 910°C to the time it takes to reach 910°C. The larger this value, the wider the process window of the heating conditions for hot stamping of structural members.

[0084] Referring to Table 2, in Example 1, the coating weight of the aluminum-based plating layer on the base material (2) was 40 g / m ２ Similarly, in Example 3, the coating mass of the aluminum-based plating layer on the base material (2) was 60 g / m ２ On the other hand, in Comparative Example 1, which has the same combination of material types as Examples 1 and 3, the coating weight of the aluminum-based plating layer on materials (1) and (2) was 80 g / m ２ In Examples 1 and 3, since the material (2) was thinly plated, the temperature rise in the overlapping portion between the material (1) and the material (2) was accelerated, and the time to complete heating of the blank was shortened compared to Comparative Example 1. As a result, in Example 1, the process window was extended by 25 seconds compared to Comparative Example 1. In Example 3, the process window was extended by 10 seconds compared to Comparative Example 1.

[0085] In Example 2, the coating weight of the aluminum-based plating layer on the base material (2) was 40 g / m ２ In Comparative Example 2, which has the same combination of material types as Example 2, the coating weight of the aluminum-based plating layer was 80 g / m on both materials (1) and (2). ２ In Example 2, since the material (2) was thinly plated, the temperature rise in the overlapping portion between the material (1) and the material (2) was accelerated, and the time to complete heating of the blank was shortened compared to Comparative Example 2. As a result, the process window in Example 2 was extended by 25 seconds compared to Comparative Example 2.

[0086] The productivity of the structural members and the greenhouse gas emission ratio were evaluated for Example 1 and Comparative Example 1. The evaluation results are shown in Table 3.

[0087]

[0088] As shown in Table 3, in Example 1, the time required to complete heating of the blank was shorter than in Comparative Example 1 (Table 2), and therefore the productivity of the structural component was improved compared to Comparative Example 1. Furthermore, in Example 1, the time required to complete heating of the blank was shorter than in Comparative Example 1, and the amount of energy consumed in manufacturing the structural component was reduced, so the greenhouse gas emission rate during manufacturing was also reduced. In Table 3, "productivity" is the number of blanks (structural components) that can be heat-treated per minute in a heating furnace. "Greenhouse gas emission rate" is the rate of greenhouse gas emission compared to Comparative Example 1. The amount of greenhouse gases generated during the heating process was calculated by allocating the power consumption per structural component to the multi-stage electric heating furnace for hot stamp blank heating at 450 kWh per hour, setting the furnace temperature at 920 °C, operating time per day at 15 hours, and heating and waiting time in the heating furnace at 3 hours, assuming component production at the productivity shown in Table 3, and multiplying it by the greenhouse gas intensity per kWh of Japan's average electricity in 2018 (from the LCA database, AIST IDEA v3.2). Other greenhouse gas emissions (other than the heating process) during the manufacture of structural components were calculated using the method described in a published literature on LCA calculations for automotive parts (Masahiro Kubo and two others, "Evaluation of Greenhouse Gas Emissions over the Life Cycle of Lightweight Steel Bodies and Parts," Spring Meeting Academic Lecture Proceedings, Society of Automotive Engineers of Japan, 2022).

[0089] Second Example The same analysis as in the first example was carried out while changing the type (material type) and thickness of the steel plate forming the structural member for the vehicle. As in the first example, the steel plate used as the material was selected from those shown in Table 1.

[0090] The analysis conditions and results of this example are shown in Table 4. As in Example 1, the raw material (1) forms the main body of the structural member, and the raw material (2) forms the reinforcing plate of the structural member. The plate thickness of the raw material (1) is 1.0 mm, and the plate thickness of the raw material (2) is 1.2 mm.

[0091]

[0092] As shown in Table 4, in Examples 4 and 5, the coefficient A of the material (1) １ is the coefficient A of material (2) ２ On the other hand, in Comparative Examples 3 and 4, the coefficient A of the material (1) is larger than １ is the coefficient A of material (2) ２ The coefficient A of the material (1) in Comparative Examples 3 and 4 is equal to １ are the coefficients A of the material (2) in Examples 4 and 5, respectively. ２ is equal to.

[0093] As described above, coefficient A corresponds to the transformation start time for each material when only the influence of elements is considered. However, the actual transformation start time for each material is also affected by the plate thickness, and becomes shorter as the plate thickness decreases. The "phase transformation start time" in Table 4 refers to the shortest time until the phase transformation to ferrite begins after the blank is heated at a furnace temperature of 920°C for 5 minutes and 30 seconds and removed from the heating furnace (the time until the thinnest material begins to transform into phase). As shown in Table 4, Examples 4 and 5 had longer phase transformation start times than Comparative Examples 3 and 4. For example, comparing Example 4 and Comparative Example 3, which are identical except for the material (1), it can be seen that Example 4 has a slower phase transformation start time than Comparative Example 3. In Example 4, coefficient A of material (1) １ is the coefficient A of material (2) ２ On the other hand, in Comparative Example 3, the coefficient A of the material (1) is larger than that of the material (2), and the hardenability of the material (1) is higher than that of the material (2). １ is the coefficient A of material (2) ２Thus, the hardenability of the material (1) is equivalent to that of the material (2). In Example 4, the hardenability of the material (1) is made higher than that of the material (2), thereby extending the phase transformation start time of the material (1) compared to Comparative Example 3, and the phase transformation start time of the material (1) and the phase transformation start time of the relatively thick material (2) are made uniform. Therefore, in Example 4, after the heating of the blank is completed, forming is easily started before the phase transformation to ferrite begins in the material (1) having a portion that does not overlap with other materials (2), making it easier for the structural member to be uniformly hardened. Even when comparing Example 5 and Comparative Example 4, which are under the same conditions except for the material (1) material, the same can be said as in Example 4 and Comparative Example 3.

[0094] The variation in martensite fraction was measured for Example 4 and Comparative Example 3. Separately, the shape accuracy of these structural members was measured. The evaluation results are shown in Table 5.

[0095]

[0096] The variation in martensite fraction was measured as follows. Ten or more analysis samples (e.g., approximately 10 mm long side) were cut out from the cross section of the structural member at the flange position of the structural member, at positions 20 mm or more away from the end and 10 mm or more away from each other. Each sample was then polished and etched with LePeller's reagent so that the observation surface was in the thickness direction. An optical microscope was then used to observe a position 1 / 4 of the way from the surface of the analysis sample in the thickness direction at 1000x magnification, and an optical microscope photograph was obtained. The obtained optical microscope photograph was subjected to image analysis using, for example, commercially available image analysis software (Photoshop CS5, manufactured by Adobe), to determine the martensite area fraction, which was then used as the martensite fraction.

[0097] As an image analysis method, the maximum brightness value L ｍａｘ and the minimum brightness value L ｍｉｎ and are obtained from the image, and the brightness is L ｍａｘ -0.3 (L ｍａｘ -L ｍｉｎ ) to L ｍａｘThe martensite fraction was measured by defining the area with pixels up to 10 as a white region and calculating the ratio of the number of pixels in the white region to the total number of pixels. This image analysis was performed on a total of 10 observation fields for each analyzed sample to determine the martensite fraction, and the average value was used as the martensite fraction for each analyzed sample. Furthermore, the difference between the maximum and minimum martensite fractions for 10 or more analyzed samples was defined as the variation in the martensite fraction in the cross section of the structural member at the flange position of the structural member.

[0098] The shape accuracy was evaluated by the distance between the structural member and the mating member at the overlapping portion when the structural member was attached to another member. In Table 5, cases where the distance from the surface of the mating member was within ±2.0 mm are marked with ○, and cases where the distance was more than ±2.0 mm but within ±3.0 mm are marked with △.

[0099] Example 4 shown in Table 5 is A １ -A ２ >0, whereas in Comparative Example 3, A １ -A ２ = 0. In Comparative Example 3, the variation in martensite fraction was 15%, whereas in Example 4, the variation in martensite fraction was reduced to 5% or less. In Example 4, the shape accuracy was also better than in Comparative Example 3.

[0100] [Example 3] A load simulation analysis was performed using general-purpose structural analysis software (LS-DYNA, manufactured by Ansys) to examine the crashworthiness of the structural members. In this analysis, an object was collided with the structural members from the side to check the deformation of the structural members. The conditions and results of this analysis are shown in Table 6.

[0101]

[0102] Referring to Table 6, the structural member according to Example 6 includes a member body and a reinforcing plate. The structural members according to Comparative Examples 5 and 6 are formed only with a member body and do not include a reinforcing plate. The structural members of Example 6 and Comparative Example 5 were manufactured by hot stamping a steel plate for hot stamping. The structural member of Comparative Example 6 was manufactured by cold pressing mild steel. In Example 6, the tensile strength of the member body and reinforcing plate after hot stamping was 1500 MPa. The tensile strength of the member body of Comparative Example 5 was 1500 MPa, and the tensile strength of the member body of Comparative Example 6 was 270 MPa. The plate thickness of the member body was 0.8 mm, and the plate thickness of the reinforcing plate was 1.0 mm.

[0103] In Example 6 and Comparative Example 6, a convex portion is provided on the bottom plate of the member body, but in Comparative Example 5, no convex portion is provided. The width of the convex portion in Example 6 is 50 mm, and the height of the convex portion is 25 mm. The width of the convex portion in Comparative Example 6 is 50 mm, and the height of the convex portion is 10 mm.

[0104] Fig. 8 is a diagram showing the deformation behavior of the structural member according to Example 6. Fig. 9 is a diagram showing the deformation behavior of the structural member according to Comparative Example 6. As shown in Fig. 8 and Table 6, in Example 6, in which a convex portion was provided on the bottom plate of the member body and the convex portion was covered with a reinforcing plate, almost no deformation occurred in the structural member even when a colliding object struck from the extension direction of the convex portion. In Example 6, a maximum load of 100 kN or more was confirmed.

[0105] On the other hand, as shown in Figure 9, in Comparative Example 6, in which a convex portion was provided on the bottom plate of the member body but no reinforcing plate was provided, deformation in which the member body was bent at the collision position of the structural member occurred. Therefore, in Comparative Example 6, the load on the structural member generated during a collision was clearly lower than in Example 6. The results for Comparative Example 5, in which no convex portion was provided on the bottom plate of the member body and no reinforcing plate was provided, were similar to those for Comparative Example 6.

[0106] This analysis confirmed that by providing a convex portion on the bottom plate of the component body and covering the convex portion with a reinforcing plate, the structural component exhibits good crashworthiness.

[0107] 100, 100A: structural member 10: member body 111, 112: vertical wall 12: bottom plate 121: protrusion 13: flange 20: reinforcing plate

Claims

1. A structural component for a vehicle comprising: a component body including a pair of opposing vertical walls and a base plate connecting the vertical walls and including a protruding portion extending from one side of the vertical walls to the other; and a reinforcing plate extending from one side of the vertical walls to the other, covering the protruding portion, and joined to the component body.

2. A structural member according to claim 1, wherein the member body is a tray for a battery box, and further includes a flange connected to each of the vertical walls on the side opposite the bottom plate and protruding outward from the member body.

3. A structural member according to claim 2, wherein said reinforcing plate further covers said flange.

4. A structural member according to claim 3, wherein the reinforcing plate is joined to the outer surface of the member body.

5. A structural member as described in claim 1, wherein the member body and the reinforcing plate are each formed of plated steel plate having a base steel plate and an aluminum-based plating layer covering both surfaces of the base steel plate, and the thickness of the aluminum-based plating layer on the reinforcing plate is smaller than the thickness of the aluminum-based plating layer on the member body.

6. A structural member according to claim 5, wherein the reinforcing plate is joined to the inner surface of the member body.

7. A structural member according to claim 1, wherein the member body and the reinforcing plate are each formed of a steel plate, and the value of coefficient A calculated by the following formula (1) using the chemical composition of the steel plate forming the member body is greater than the value of coefficient A calculated by the following formula (1) using the chemical composition of the steel plate forming the reinforcing plate: A = 1.48 x (2.7 x C + 0.4 x Si + Mn + 0.45 x Ni + 0.8 x Cr + 2 x Mo). ３．４２ (1) In the above formula (1), the element symbols are substituted with the contents (mass%) of the corresponding elements.

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