Tubular members and structures including tubular members

Abstract

To provide a tubular member that includes a steel part and a light metal part joined to each other and of which application is less likely to be limited, and to provide a structure including the tubular member.SOLUTION: A tubular member (10) includes a steel part (11), a light metal part (12), and a welded part (14). The light metal part (12) is arranged while being aligned with the steel part (11) in an axial direction of the tubular member (10). The light metal part (12) is joined to the steel part (11). The welded part (14) extends in the axial direction of the tubular member (10) while straddling the steel part (11) and the light metal part (12).SELECTED DRAWING: Figure 6B

Description

Technical Field

[0005] , ,

[0001] The present disclosure relates to a tubular member and a structure including the tubular member.

Background Art

[0002] Conventionally, in structures included in an automobile body or the like, in addition to members formed by pressing a plate material, tubular members are also used. When weight reduction is required for a tubular member, a light metal having a specific gravity smaller than that of steel may be used as the material of the tubular member. However, if the entire tubular member is formed of a light metal, the strength of the tubular member decreases as compared with the case where the tubular member is formed of steel. When strength is also required for the tubular member, it is necessary to increase the thickness of the tubular member to make it larger, and the degree of freedom in arranging the tubular member in the structure decreases.

[0003] In order to suppress the increase in size of the tubular member, it is conceivable to use both steel and a light metal for the tubular member. For example, Patent Document 1 discloses a technique for forming a tubular member by joining a steel pipe and an aluminum alloy hollow member. In Patent Document 1, the end face of the steel pipe and the end face of the aluminum alloy hollow member are abutted against each other, and while applying a frictional pressure to the steel pipe and the aluminum alloy hollow member, the aluminum alloy hollow member is relatively rotated around the axis with respect to the steel pipe. Thereby, the end face of the steel pipe and the end face of the aluminum alloy hollow member are frictionally pressure-bonded.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the technology described in Patent Document 1, the end face of a steel pipe and the end face of a light metal pipe, which is a hollow aluminum alloy member, are joined by friction welding. Therefore, the steel pipe and the light metal pipe are arranged coaxially and rotated relative to each other around the axis. For this reason, at least the end faces of the steel pipe and the light metal pipe must be circular in diameter. The technology in Patent Document 1 cannot manufacture a tubular member where the joint between the steel pipe and the light metal pipe is non-circular in cross-section. Furthermore, even if the tubular member is processed from a circular pipe to a non-circular pipe after friction welding, it is difficult to obtain the desired cross-sectional shape with high accuracy. Consequently, there is a problem in that the shape of the tubular member is limited, and its applications are restricted.

[0006] The object of this disclosure is to provide a tubular member that includes joined steel and light metal parts and is not easily restricted in its use, and a structure including the tubular member. [Means for solving the problem]

[0007] The tubular member according to this disclosure comprises a steel portion, a light metal portion, and a welded portion. The light metal portion is arranged alongside the steel portion in the axial direction of the tubular member. The light metal portion is joined to the steel portion. The welded portion extends axially of the tubular member, spanning both the steel portion and the light metal portion. [Effects of the Invention]

[0008] According to this disclosure, it is possible to provide a tubular member that includes joined steel and light metal parts and is not easily limited in its application. Furthermore, this tubular member can be applied to various structures. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a side view of a structure according to an embodiment. [Figure 2] Figure 2 shows an example of a joining method between a steel portion and a light metal portion in a tubular member according to the embodiment. [Figure 3] Figure 3 shows another example of the joining method between the steel portion and the light metal portion in the tubular member according to the embodiment. [Figure 4]Figure 4 shows yet another example of the joining method between the steel portion and the light metal portion in the tubular member according to the embodiment. [Figure 5] Figure 5 is a cross-sectional view of the joint between the steel portion and the light metal portion in a tubular member according to the embodiment. [Figure 6A] Figure 6A is a schematic diagram illustrating an example of a method for manufacturing a tubular member according to the embodiment. [Figure 6B] Figure 6B is a schematic diagram illustrating an example of a method for manufacturing a tubular member according to the embodiment. [Figure 6C] Figure 6C is a schematic diagram illustrating an example of a method for manufacturing a tubular member according to the embodiment. [Figure 6D] Figure 6D is a schematic diagram illustrating an example of a method for manufacturing a tubular member according to the embodiment. [Modes for carrying out the invention]

[0010] The tubular member according to this embodiment comprises a steel portion, a light metal portion, and a welded portion. The light metal portion is arranged alongside the steel portion in the axial direction of the tubular member. The light metal portion is joined to the steel portion. The welded portion extends axially across the steel portion and the light metal portion of the tubular member (first configuration).

[0011] In the tubular member relating to the first configuration, the welded portion extends axially across the steel portion and the light metal portion. Such a tubular member can be manufactured by rolling the joined steel plate and light metal plate into a tube. That is, after the steel plate and light metal plate are bent so that their side edges are close together, the side edges along the direction in which the steel plate and light metal plate are aligned are welded together to produce a tubular member in which a welded portion extending across the steel portion and the light metal portion is formed. In this case, the cross-section of the joint between the steel portion and the light metal portion does not need to be circular, and tubular members with various cross-sectional shapes can be easily and accurately formed. In other words, a tubular member with a wide range of applications can be obtained.

[0012] The tubular member according to the first configuration includes a steel part and a light metal part. In this case, while reducing the weight of the tubular member with the light metal part, the strength of the tubular member can be ensured with the steel part. In a part of the tubular member where particularly high strength is required, a steel part with high material strength may be arranged, so there is no need to make the tubular member overly thick for the purpose of ensuring strength. Therefore, the increase in size of the tubular member is suppressed, and the degree of freedom in arranging the tubular member in the structure can be increased.

[0013] The welded part may extend over the entire lengths of the steel part and the light metal part in the axial direction of the tubular member (second configuration).

[0014] When the tubular member according to the embodiment is manufactured, the side edges located on both sides of the joint between the steel plate and the light metal plate are welded, so that the steel plate and the light metal plate become the steel part and the light metal part of the tubular member, respectively, and a welded part extending across the steel part and the light metal part is formed. In the second configuration, this welded part extends over the entire lengths of the steel part and the light metal part of the tubular member. That is, the steel part and the light metal part of the tubular member have a closed cross-section as a whole. Thereby, the rigidity of the tubular member can be improved.

[0015] In the tubular member according to the first or second configuration, the steel part may include a curved part extending along the axial direction of the tubular member (third configuration).

[0016] The tubular member according to any one of the first to third configurations may have a non-circular cross-section at the joint between the steel part and the light metal part (fourth configuration).

[0017] In the tubular member according to any one of the first to fourth configurations, the steel part may include a quenched part provided on at least a part of the steel part (fifth configuration).

[0018] In the fifth configuration, at least a part of the steel part is quenched. Thereby, the strength of the steel part included in the tubular member can be further increased. Therefore, it becomes possible to reduce the thickness of the steel part while ensuring the strength of the steel part, and the weight of the tubular member can be reduced.

[0019] In the tubular member according to the fifth configuration, the steel part can further include a non-hardened part. The non-hardened part is, for example, disposed on the side of the light metal part with respect to the hardened part. The non-hardened part may be adjacent to the joint between the steel part and the light metal part (sixth configuration).

[0020] In the sixth configuration, in the steel part, the region adjacent to the joint between the steel part and the light metal part is not hardened. Therefore, the heat during hardening hardly affects the joint between the steel part and the light metal part, and the strength of the joint can be ensured.

[0021] The structure according to the seventh configuration includes a tubular member according to any one of the first to sixth configurations and a joined member. The joined member is made of a material mainly composed of the same metal as the light metal part in the tubular member. The light metal part is joined to the joined member.

[0022] The structure according to the eighth configuration includes a tubular member according to any one of the first to sixth configurations and a joined member. The joined member is made of steel. The steel part in the tubular member is joined to the joined member.

[0023] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The same or corresponding components in each figure are denoted by the same reference numerals, and the same description will not be repeated.

[0024] [Configuration of Structure Including Tubular Member] FIG. 1 is a side view of a structure 100 according to the present embodiment. FIG. 1 shows an example of the structure 100 used for an automobile body. However, the structure 100 may be used other than for an automobile body. The structure 100 includes a tubular member 10 and a joined member 20.

[0025] In the example of the present embodiment, the tubular member 10 is a skeletal part of an automobile. FIG. 1 shows an A-pillar upper as an example of the tubular member 10. The tubular member 10 includes a steel part 11 and a light metal part 12.

[0026] The steel portion 11 is provided in the part of the tubular member 10 where relatively high strength is required. Since the steel portion 11 is part of the tubular member 10, it has a tubular shape. The steel portion 11 may have a circular cross-section, or it may have a non-circular cross-section, such as a polygon. The cross-section of the steel portion 11 is the cross-section obtained when the steel portion 11 is cut by a plane perpendicular to the axial direction of the tubular member 10.

[0027] The steel portion 11 extends in the axial direction of the tubular member 10. In the example shown in Figure 1, the steel portion 11 includes a curved portion 111 that extends along the axial direction of the tubular member 10. The curved portion 111 is provided on at least a part of the steel portion 11.

[0028] The light metal part 12 is provided in the tubular member 10 in a part where strength is not required compared to the steel part 11. Since the light metal part 12 is part of the tubular member 10, it has a tubular shape. The light metal part 12 is made of a metal material with a lower specific gravity than the steel material that makes up the steel part 11. Examples of this metal material include aluminum-based materials, magnesium-based materials, titanium-based materials, etc. The light metal part 12 may be made of aluminum, magnesium, or titanium, or an alloy of any of these. Typically, the light metal part 12 is an aluminum alloy tube. The light metal part 12 may be a 5000 series, 6000 series, or 7000 series aluminum alloy tube.

[0029] The light metal part 12 may have a circular cross-section, or it may have a non-circular cross-section, such as a polygon. The cross-section of the light metal part 12 is the cross-section obtained when the light metal part 12 is cut by a plane perpendicular to the axial direction of the tubular member 10.

[0030] The light metal portion 12 is arranged alongside the steel portion 11 in the axial direction of the tubular member 10. The light metal portion 12 is joined to the steel portion 11. More specifically, the end of the light metal portion 12 is joined to the end of the steel portion 11.

[0031] The end of the light metal part 12 can be joined to the end of the steel part 11 in various ways. Examples of joining methods between the steel part 11 and the light metal part 12 are shown in Figures 2 to 4. Figures 2 to 4 are cross-sectional views (longitudinal cross-sectional views) of the tubular member 10 when it is cut along its central axis, showing the joint 13 between the steel part 11 and the light metal part 12 and its vicinity.

[0032] As shown in Figure 2, the light metal part 12 may be butt-joined with the steel part 11. That is, the end face of the steel part 11 and the end face of the light metal part 12 may be butt-joined together. In the example in Figure 2, the thickness of the steel part 11 and the thickness of the light metal part 12 are equal. However, the thickness of the steel part 11 may be different from the thickness of the light metal part 12.

[0033] As shown in Figure 3, the light metal part 12 may be joined to the steel part 11 by overlapping. That is, the end of the light metal part 12 may be inserted into the end of the steel part 11, and the ends may be joined in an overlapping state. Alternatively, the end of the steel part 11 may be inserted into the end of the light metal part 12, and the ends may be joined by overlapping. In the example in Figure 3, the thickness of the light metal part 12 is greater than the thickness of the steel part 11 in order to reduce the difference in strength between the steel part 11 and the light metal part 12. However, the thickness of the light metal part 12 may be equal to the thickness of the steel part 11, or it may be less than the thickness of the steel part 11.

[0034] As shown in Figure 4, one end of the steel part 11 and the light metal part 12 can be cut out, and the other end can be placed in the cutout. In the example in Figure 4, the thickness of the light metal part 12 is greater than the thickness of the steel part 11, and a notch is formed at the end of the light metal part 12. However, the thickness of the light metal part 12 may be less than the thickness of the steel part 11, and a notch may be formed at the end of the steel part 11.

[0035] Figure 5 is a cross-sectional view (transverse plane) of the joint 13 between the steel part 11 and the light metal part 12 when cut by a plane perpendicular to the axial direction of the tubular member 10. In this embodiment, the tubular member 10 has a non-circular cross-section at the joint 13. In Figure 5, the joint 13 has a substantially rectangular cross-section. However, the cross-sectional shape of the joint 13 may be a quadrilateral other than a rectangle, such as a square, parallelogram, or rhombus, or it may be another polygon. The cross-sectional shape of the joint 13 may also be circular. The cross-sectional shape of the joint 13 is not particularly limited.

[0036] Returning to Figure 1, the steel portion 11 may include a hardened portion 112 and an unhardened portion 113. The hardened portion 112 is the part of the steel portion 11 that has been hardened. In the hardened portion 112, the hardening is applied to the entire circumferential direction of the steel portion 11. The hardened portion 112 is provided, for example, at a distance from the joint 13 between the steel portion 11 and the light metal portion 12 in the axial direction of the tubular member 10.

[0037] The unhardened portion 113 is the part of the steel portion 11 that has not been hardened. The unhardened portion 113 is located on the light metal portion 12 side relative to the hardened portion 112. The unhardened portion 113 is adjacent to the joint 13 between the steel portion 11 and the light metal portion 12. The hardness of the hardened portion 112 is greater than the hardness of the unhardened portion 113. For example, the Vickers hardness of the hardened portion 112 measured with a test force of 1 kgf in a Vickers hardness test compliant with JIS Z 2244:2009 is 350 HV or higher.

[0038] Continuing to refer to Figure 1, the tubular member 10 is joined to the member to be joined 20. In the example in Figure 1, the member to be joined 20 is the lower A pillar. The light metal portion 12 of the tubular member 10 is joined to the member to be joined 20. The light metal portion 12 is joined to the member to be joined 20 at the end opposite to the joint 13 with the steel portion 11. The light metal portion 12 is typically joined to the member to be joined 20 by welding.

[0039] The member to be joined 20 is made of a metallic material with a lower specific gravity than steel. The member to be joined 20 is made of, for example, an aluminum-based material, a magnesium-based material, or a titanium-based material. However, the member to be joined 20 is made of a material whose main component is the same metal as the light metal part 12. For example, if the light metal part 12 is made of an aluminum-based material, the member to be joined 20 is also made of an aluminum-based material. The material of the member to be joined 20 does not need to be exactly the same as the material of the light metal part 12; it is sufficient if it is a metallic material of the same type as the light metal part 12. The member to be joined 20 may be, for example, an aluminum die-cast product (ADC material) or an aluminum casting (AC material). Alternatively, the member to be joined 20 may be a press-formed or extruded product made of 5000 series, 6000 series, or 7000 series aluminum alloy.

[0040] [Method for manufacturing tubular members] Next, an example of a method for manufacturing the tubular member 10 will be described with reference to Figures 6A to 6D. As shown in Figures 6A to 6D, the method for manufacturing the tubular member 10 may include the steps of preparing a sheet material 30, forming the sheet material 30 into a tubular member 10, and bending the tubular member 10.

[0041] Referring to Figure 6A, in the manufacture of the tubular member 10 (Figure 1), a plate material 30 is first prepared. The plate material 30 includes a steel plate 31, a light metal plate 32, and a joint 13.

[0042] The steel plate 31 and the light metal plate 32 are joined to each other at a joint 13. The joint 13 extends across the plate material 30 between the side edges 34 and 35 of the plate material 30. The method of joining the steel plate 31 and the light metal plate 32 is not particularly limited, as long as it is capable of joining dissimilar materials. The steel plate 31 and the light metal plate 32 are joined by a solid-state joining method, preferably one in which the melting of the steel material and the light metal material does not substantially occur, such as friction stir welding (FSW) or ultrasonic welding. However, the steel plate 31 and the light metal plate 32 may also be joined by mechanical joining, such as self-piercing rivets (SPR), or by using an adhesive, or by brazing. Alternatively, the steel plate 31 and the light metal plate 32 may be joined by welding, which causes melting of the steel material and / or the light metal material, as long as it is possible to join the two.

[0043] Referring to Figure 6B, the plate material 30 is formed into a tubular member 10. The plate material 30 is bent into a tubular shape so that the side edges 34 and 35 (Figure 6A) on both sides of the joint 13 are close together. For example, when forming the plate material 30 into a polygonal tube, the plate material 30 can be bent using a press brake. After that, the side edges 34 and 35 of the plate material 30 can be welded to obtain the tubular member 10. Alternatively, the plate material 30 may be formed into a tubular member 10 using a known or commercially available pipe-making device.

[0044] By welding the side edges 34 and 35 of the plate material 30, the steel plate 31 and the light metal plate 32 become the steel portion 11 and the light metal portion 12 of the tubular member 10, respectively. Figure 6B shows an example where the tubular member 10 is a rectangular pipe. However, the tubular member 10 may be a non-circular pipe other than a rectangular pipe. It is also possible for the tubular member 10 to be a circular pipe.

[0045] The tubular member 10 is provided with a welded portion 14 by welding the side edges 34 and 35 of the plate material 30. From the viewpoint of improving the rigidity of the tubular member 10, it is preferable that the welded portion 14 is formed by continuous welding, such as arc welding or laser welding. The welded portion 14 extends in the axial direction of the tubular member 10, spanning the steel portion 11 and the light metal portion 12. It is preferable that the welded portion 14 extends along the entire length of the steel portion 11 and the light metal portion 12 in the axial direction of the tubular member 10. However, it is not always necessary for the welded portion 14 to be provided along the entire length of the steel portion 11 and the light metal portion 12. For example, the welded portion 14 does not need to be present at the end of the light metal portion 12 on the side opposite to the steel portion 11. However, when quenching is performed on the steel portion 11 as described later, it is necessary to provide a continuous welded portion 14 along the entire length of the quenched area in order to avoid the concentration of current density when induction heating is performed with a heating coil. If the tubular member 10 is a polygonal tube, it is preferable that the welded portion 14 is located at a location other than the corners of the tubular member 10.

[0046] In the example shown in Figure 6B, the weld 14 extends parallel to the axial direction of the tubular member 10. However, the weld 14 may be inclined with respect to the axial direction of the tubular member 10. The weld 14 only needs to extend substantially or generally axially across both the steel portion 11 and the light metal portion 12. The weld 14 extends intersecting the joint 13 between the steel portion 11 and the light metal portion 12.

[0047] In this embodiment, the tubular member 10 is bent. More specifically, the steel portion 11 of the tubular member 10 is bent. The tubular member 10 is bent using a processing device 40, for example, schematically shown in Figure 6C. The processing device 40 is capable of performing three-dimensional hot bending and quenching (3DQ) on the workpiece.

[0048] The processing apparatus 40 includes an extruder 41, a plurality of support rollers 42, a movable roller die 43, a high-frequency heating coil 44, and a cooling device 45. The extruder 41 is configured to feed the tubular member 10 as the workpiece continuously or intermittently. The plurality of support rollers 42 are located downstream of the extruder 41 in the feeding direction of the tubular member 10. The support rollers 42 are configured to support the tubular member 10. The movable roller die 43 clamps the tubular member 10 downstream of the support rollers 42. The high-frequency heating coil 44 is located between the support rollers 42 and the movable roller die 43. The cooling device 45 is configured to spray a refrigerant (cooling water) onto the tubular member 10.

[0049] The processing apparatus 40 bends the steel part 11 while feeding the tubular member 10 with the extrusion apparatus 41. The steel part 11 is locally heated by the high-frequency heating coil 44 and then water-cooled and hardened by the cooling apparatus 45. At the same time, a bending moment is applied by the movable roller die 43 to the part of the steel part 11 that has become hot and has reduced deformation resistance, causing that part to undergo plastic deformation.

[0050] Referring to Figure 6D, in the tubular member 10 after bending, a curved portion 111 is formed in the steel portion 11. In addition, a hardened portion 112 is formed in the steel portion 11. When the curved portion 111 is formed in the steel portion 11 by 3DQ, the curved portion 111 is provided in the hardened portion 112. The hardened portion 112 is positioned away from the joint portion 13 to such an extent that the effects of the heat during hardening do not extend to the joint portion 13. The portion adjacent to the joint portion 13 between the steel portion 11 and the light metal portion 12 is the non-hardened portion 113.

[0051] The tubular member 10 may be further processed as needed. For example, the steel portion 11 may be processed by hydroforming. Alternatively, at least one of the steel portion 11 and the light metal portion 12 may be subjected to cold bending, pressing, or the like. These processes can be carried out at any time during the manufacturing process of the tubular member 10. Furthermore, if a curved portion 111 is formed by cold working, the curved portion 111 can be positioned at any location on the tubular member 10.

[0052] [effect] The tubular member 10 according to this embodiment includes a welded portion 14 that extends axially across the steel portion 11 and the light metal portion 12. The tubular member 10 is manufactured by joining a steel plate 31 before it becomes the steel portion 11 and a light metal plate 32 before it becomes the light metal portion 12 to form a plate material 30, processing the plate material 30 into a tubular shape, and welding the side edges 34 and 35. In this case, even a tubular member 10 having a non-circular cross-section can be easily formed. Therefore, the shape of the tubular member 10 has a high degree of freedom, and the applications of the tubular member 10 are not easily restricted.

[0053] For example, when a circular steel pipe and a circular light metal pipe are integrated to form a tubular member, and then this tubular member is processed to have a non-circular cross-section, it is difficult to ensure the flatness of the planar portion, resulting in a decrease in the shape accuracy of the tubular member. Furthermore, roll forming is essential to deform the circular tubular member into a non-circular pipe, requiring dedicated pipe manufacturing equipment for roll forming, which increases equipment costs. In contrast, in this embodiment, a steel plate 31 and a light metal plate 32 are joined to form a plate material 30, and then the plate material 30 is formed into a tubular member 10 by so-called plate-rolled pipe forming. Therefore, if a planar portion exists in the tubular member 10, the flatness of the planar portion is easily ensured, and the tubular member 10 can be manufactured with good shape accuracy. In addition, since plate-rolled pipe forming can be carried out using a general press brake, equipment costs can also be reduced.

[0054] Generally, joining pipes together is difficult, and especially when joining pipes made of different materials, the available methods are limited. However, in this embodiment, since the steel plate 31 before it becomes the steel portion 11 of the tubular member 10 and the light metal plate 32 before it becomes the light metal portion 12 of the tubular member 10, that is, plate-like members are joined together, joining is easy and various joining methods can be employed.

[0055] In this embodiment, it is preferable that the joint 13 between the steel portion 11 and the light metal portion 12 is joined in such a way that substantially no melting occurs of the steel plate 31 and the light metal plate 32. That is, it is preferable that the joint 13 is formed by a method other than fusion welding. If the steel plate 31 and the light metal plate 32 do not melt during joining, intermetallic compounds are not formed at the joint 13, or if they are formed, only in trace amounts, thus suppressing embrittlement or corrosion of the tubular member 10 caused by intermetallic compounds.

[0056] As described above, the joint 13 between the steel part 11 and the light metal part 12 can also be formed by mechanical joining. However, when forming the joint 13 using self-piercing rivets, it is preferable that rivets are not placed at the corners of the tubular member 10. Since mechanical joining uses components such as self-piercing rivets, from the viewpoint of reducing the weight of the tubular member 10, it is preferable to form the joint 13 by a joining method other than mechanical joining.

[0057] In the tubular member 10 according to this embodiment, steel parts 11 are provided in areas where relatively high strength is required, and light metal parts 12 are provided in areas where strength is not so required. Therefore, the tubular member 10 can be made lighter with the light metal parts 12 while ensuring the desired strength with the steel parts 11. Since the steel parts 11, which have high material strength, are provided in areas of the tubular member 10 where particularly high strength is required, there is no need to make the tubular member 10 excessively thick in order to ensure strength. Therefore, it becomes easier to arrange the tubular member 10 in, for example, the body of an automobile.

[0058] In this embodiment, the welded portion 14 extends along the entire length of the steel portion 11 and the light metal portion 12. That is, the steel portion 11 and the light metal portion 12 have a closed cross-section throughout. This increases the rigidity of the tubular member 10.

[0059] In the tubular member 10 according to this embodiment, a hardened portion 112 is provided in at least a part of the steel portion 11. The hardened portion 112 is a part whose hardness has been increased by the hardening treatment, and the strength of the steel portion 11 can be improved. Therefore, even if the steel portion 11 is made thinner, the strength of the steel portion 11 can be ensured, and the weight of the tubular member 10 can be reduced.

[0060] In the tubular member 10 according to this embodiment, a non-hardened portion 113 is provided in the portion of the steel portion 11 adjacent to the joint portion 13 between the steel portion 11 and the light metal portion 12. The non-hardened portion 113 is positioned between the hardened portion 112 and the joint portion 13. Therefore, the effect of heat during hardening on the joint portion 13 is small, and the strength of the joint portion 13 can be ensured. Furthermore, it is possible to prevent the effect of heat during hardening from extending to the light metal portion 12.

[0061] While embodiments relating to this disclosure have been described above, this disclosure is not limited to the embodiments described above, and various modifications are possible as long as they do not deviate from its spirit.

[0062] In the above embodiment, an example is described in which the tubular member 10 is the upper A-pillar and the member to be joined 20 is the lower A-pillar. However, the tubular member 10 can also be applied to parts other than the upper A-pillar. For example, the tubular member 10 may be a side sill and the member to be joined 20 may be a B-pillar. In this case, the member to be joined 20 may be made of steel, and the steel portion 11 of the tubular member 10 may be joined to the member to be joined 20 by, for example, welding. However, the use of the tubular member 10 is not limited to this. The tubular member 10 may be other automotive frame parts or may be used for purposes other than the automobile body. When the steel portion 11 of the tubular member 10 is joined, the member to be joined 20 is made of steel, and when the light metal portion 12 is joined, it is made of a material whose main component is the same metal as the light metal portion 12.

[0063] In the above embodiment, the steel portion 11 of the tubular member 10 is bent by 3DQ, forming a curved portion 111. However, the steel portion 11 may be bent by a method other than 3DQ. Alternatively, the steel portion 11 may not be bent, and the curved portion 111 may not exist in the steel portion 11. Furthermore, the hardened portion 112 may not exist in the steel portion 11.

[0064] In the above embodiment, the length of the steel portion 11 in the axial direction of the tubular member 10 is greater than the length of the light metal portion 12. However, the length of the steel portion 11 may be equal to the length of the light metal portion 12, or it may be shorter than the length of the light metal portion 12.

[0065] The tubular member 10 according to the above embodiment includes a single steel portion 11 and a single light metal portion 12. However, the tubular member 10 may include multiple steel portions 11. Furthermore, the tubular member 10 may also include multiple light metal portions 12. [Explanation of Symbols]

[0066] 10: Tubular member 11: Steel section 111: Curved section 112: Hardened section 113: Non-hardened part 12: Light Metals Division 13:Joint part 14: Welded section

Claims

1. A tubular member, Steel parts and, A light metal portion is arranged alongside the steel portion in the axial direction of the tubular member and is joined to the steel portion, A welded portion extending in the axial direction across the steel portion and the light metal portion, Equipped with, The steel portion is a tubular member comprising a hardened portion provided on at least a part of the steel portion and a non-hardened portion located on the light metal portion side relative to the hardened portion and adjacent to the joint between the steel portion and the light metal portion.

2. A tubular member according to claim 1, The welded portion is a tubular member that extends along the entire length of the steel portion and the light metal portion in the axial direction.

3. A tubular member according to claim 1, The steel portion is a tubular member including a curved portion extending along the axial direction.

4. A tubular member according to claim 1, The tubular member has a non-circular cross-section at the joint between the steel portion and the light metal portion.

5. It is a structure, A tubular member according to any one of claims 1 to 4, A member to be joined, which is made of a material whose main component is the same metal as the light metal portion in the tubular member, and to which the light metal portion is joined, A structure that includes the following features.

6. It is a structure, A tubular member according to any one of claims 1 to 4, A member to be joined, which is made of steel and to which the steel portion of the tubular member is joined, A structure that includes the following features.

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