Method for manufacturing arc-welded joint, arc-welded joint, and automotive component

Abstract

The invention relates to a method for manufacturing an arc-welded joint, an arc-welded joint, and an automotive component. A method for manufacturing an arc welded joint according to one embodiment of the present invention includes: overlapping a first steel plate and a second steel plate in a plate thickness direction so that an end portion of the first steel plate is disposed on a surface of the second steel plate; and forming a weld bead by arc welding the end of the first steel plate and the surface of the second steel plate having a zinc plating layer on the surface thereof, the arc welding being yaw bar arc welding in which a welding torch is periodically swung in a direction transverse to the welding direction. The plate thickness tL (mm) of the second steel plate and the wavelength y (mm) of the waveform of the welding torch in the yaw bar arc welding are set to values satisfying y / tL < = 2.8, the width w (mm) of the bead and the plate thickness tL of the second steel plate are set to values satisfying 3.3 < = w / tL < = 7.0, and the droplet transition frequency D (times / sec) and the swing frequency f (Hz) from the welding torch to the molten pool in the yaw bar arc welding are set to values satisfying D / f > = 25.

Description

Technical Field

[0001] The invention relates to a method for manufacturing an arc welding joint, an arc welding joint and an automobile component.

[0002] This application claims priority based on Tokugan Application No. 2022-098078 filed in Japan on June 17, 2022, the contents of which are incorporated herein by reference. Background Art

[0003] The materials of automobile parts such as chassis are mainly hot-rolled thin steel plates. Hot-rolled thin steel plates are often joined by arc welding.

[0004] In recent years, as the strength and thickness of steel sheets constituting automobile parts have increased, the level of corrosion resistance required for welded joints has also increased. Therefore, there is an increasing demand for using galvanized steel sheets with excellent corrosion resistance as materials for automobile parts.

[0005] It is known that when arc welding is performed on galvanized steel sheets, voids called porosity defects are easily generated in the weld bead. Figure 3 As shown, during normal arc welding, the zinc-based coating 14 having a lower melting point and boiling point than iron evaporates to form zinc vapor 14v. When the molten pool 13P solidifies while the zinc vapor 14v remains in the molten pool 13P, a porosity defect pd is generated in the weld bead 13. The molten pool 13P refers to a pool of molten metal formed by heat of an arc or the like during welding.

[0006] exist Figure 6 An example of an X-ray image of a conventional arc welded joint having a porosity defect is shown in FIG. Figure 6 In the arc welded joint shown in the image of FIG. 1 , a large number of porosity defects pd shown in dark colors are contained inside the weld bead 13 shown in bright colors.

[0007] If a large number of pore defects are generated, the joint area of ​​the steel plates is reduced, thereby reducing the joint strength. In addition, pore defects generate pits that reduce the electro-deposition coating properties. Pits are pores that reach the surface of the weld bead and open. The pits make the surface of the weld bead uneven and may cause electro-deposition coating defects. Even if the pore defects are small, the electro-deposition coating properties will be reduced.

[0008] For the reasons described above, there is a demand for a technique for suppressing the occurrence of porosity defects in welded joints obtained by arc welding galvanized steel sheets.

[0009] Patent document 1 discloses a TIG welding method for fillet weld joints using galvanized steel sheets or primer-coated steel sheets, characterized in that a TIG arc oscillating at a frequency of 10 Hz or more and an amplitude of 3 mm or more is used, and welding conditions including an arc current value and a welding speed are adopted so that the base material surfaces constituting the overlap joint of two base materials are melted but the joint corner is not melted, and an additional welding wire is fed from the welding direction along the base material corner toward the molten pool to form a deposited metal, while a gap is formed at the joint corner by the welding wire and the base material, and the zinc vapor generated on the base material surface near the joint corner near the bottom of the molten pool is released from the above-mentioned gap to the outside while welding is performed. According to this welding method, by always maintaining a path that allows zinc vapor or primer component vapor from the heat-affected zone region adjacent to the molten pool of the closely attached base material overlapping portion of the galvanized steel sheet or primer-coated steel sheet to be easily discharged to the outside air, welding can be performed without forming pores or pits.

[0010] Prior art literature

[0011] Patent Literature

[0012] Patent Document 1: Japanese Patent Application Publication No. 2003-53544 Summary of the invention

[0013] Problems to be solved by the invention

[0014] However, in the technology disclosed in Patent Document 1, it is necessary to prevent the corners of the joint from melting. Therefore, according to the technology of Patent Document 1, it is difficult to ensure the penetration depth of the weld. In addition, in the technology disclosed in Patent Document 1, the welding method must be tungsten inert gas (TIG) welding. Tungsten inert gas (TIG) welding is an arc welding in which non-consumable tungsten is used as an electrode to generate an arc and filler materials such as welding wire are put into the arc. The technology disclosed in Patent Document 1 cannot be applied to consumable electrode arc welding such as submerged arc welding. In order to suppress the occurrence of porosity defects in various components, a technology that is not limited to tungsten inert gas (TIG) welding but can be applied to various arc welding is required.

[0015] An object of the present invention is to provide a method for producing an arc welded joint capable of suppressing porosity defects in welding of galvanized steel sheets, an arc welded joint made of galvanized steel sheets and suppressing porosity defects, and an automobile component.

[0016] Means for solving problems

[0017] The gist of the present invention is as follows.

[0018] (1) A method for manufacturing an arc welding joint according to one embodiment of the present invention comprises: overlapping the first steel plate and the second steel plate in a plate thickness direction in such a manner that an end of the first steel plate is arranged on a surface of the second steel plate; and arc welding the overlapped end of the first steel plate and the surface of the second steel plate to form a weld bead, wherein the surface of the second steel plate has a zinc coating, and the arc welding is a horizontal movement of the welding torch in which the welding torch is periodically swung in a direction transverse to the welding direction. Arc welding, the thickness tL (mm) of the second steel plate and the wavelength y (mm) of the waveform of the welding torch in the oscillating arc welding are set to values ​​satisfying y / tL≤2.8, the width w (mm) of the weld bead and the thickness tL of the second steel plate are set to values ​​satisfying 3.3≤w / tL≤7.0, and the droplet transfer frequency D (times / second) from the welding torch to the molten pool and the oscillation frequency f (Hz) in the oscillating arc welding are set to values ​​satisfying D / f≥25.

[0019] (2) In the method for producing an arc welded joint according to (1) above, preferably, the Si content of the weld bead is set to 0.5 mass % or less.

[0020] (3) Preferably, in the method for manufacturing an arc welded joint described in (1) or (2), the wavelength y of the waveform of the welding torch and the plate thickness tL of the second steel plate are set to values ​​satisfying 0.7≤y / tL.

[0021] (4) Preferably, in the method for manufacturing an arc welded joint as described in any one of (1) to (3) above, the weld bead does not penetrate the second steel plate in the plate thickness direction.

[0022] (5) Preferably, in the method for manufacturing an arc welded joint described in any one of (1) to (4), in a cross section along the plate thickness direction, an outer edge of the weld bead intersects with a butt surface between the first steel plate and the second steel plate.

[0023] (6) In the method for manufacturing an arc welded joint described in any one of (1) to (5), preferably, the oscillation frequency f is less than 10 Hz.

[0024] (7) Preferably, in the method for manufacturing an arc welded joint according to any one of (1) to (6), the arc welding is metal active gas (MAG) welding.

[0025] (8) Another embodiment of the arc welding joint of the present invention comprises: a first steel plate portion; a second steel plate portion overlapping with the first steel plate portion in the plate thickness direction; and a weld bead connecting an end portion of the first steel plate portion arranged on the surface of the second steel plate portion with the surface of the second steel plate portion, a zinc-based coating is present in an area of ​​the surface of the second steel plate portion where the weld bead is not provided, a width w of the weld bead and a plate thickness tL of the second steel plate portion satisfy 3.3≤w / tL≤7.0, and a porosity defect rate of a stable portion of the weld bead is less than 10%.

[0026] (9) In the arc welded joint described in (8) above, preferably, the Si content of the weld bead is 0.5 mass % or less.

[0027] (10) Preferably, in the arc welding joint described in (8) or (9), in the stable portion of the weld bead, the weld toe on the side of the second steel plate portion has a wavy shape, and the wavelength Y of the weld toe and the plate thickness tL of the second steel plate portion satisfy 0.7≤Y / tL≤2.8.

[0028] (11) Preferably, in the arc welded joint described in any one of (8) to (10), the weld bead does not penetrate the second steel plate portion in the plate thickness direction.

[0029] (12) Preferably, in the arc welded joint described in any one of (8) to (11), in a cross section along the plate thickness direction, an outer edge of the weld bead intersects with a butt surface between the first steel plate portion and the second steel plate portion.

[0030] (13) An automobile component according to another aspect of the present invention includes the arc welding joint described in any one of (8) to (12).

[0031] Effects of the Invention

[0032] According to the present invention, it is possible to provide a method for manufacturing an arc welded joint capable of suppressing porosity defects in welding of galvanized steel sheets, and an arc welded joint composed of galvanized steel sheets and suppressing porosity defects. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a conceptual diagram of a method for manufacturing an arc welding joint according to the present embodiment in a plan view.

[0034] Figure 2 This is a conceptual diagram of the method for manufacturing an arc welded joint according to the present embodiment in a cross section perpendicular to the welding direction.

[0035] Figure 3 This is a cross-sectional view of an arc welded joint with porosity defects in the weld bead.

[0036] Figure 4 It is a top view of an example of the arc welding head according to the present embodiment.

[0037] Figure 5 This is an X-ray image of an example of the arc welding joint according to the present embodiment.

[0038] Figure 6 This is an X-ray image of an example of a conventional arc welded joint including a porosity defect.

[0039] Figure 7 This is a plan view of an example of a weld bead in which the weld toe of the stabilizing portion has a wavy shape.

[0040] Fig. 8A This is a cross-sectional view of an example of an arc welded joint having a gap near the root R.

[0041] Figure 8B This is a cross-sectional view of an example of an arc welded joint in which the outer edge of a weld bead intersects the butting surface of a first steel plate portion and a second steel plate portion. DETAILED DESCRIPTION

[0042] For example, Figure 1 as well as Figure 2As shown, a manufacturing method of an arc welding joint 1 according to one embodiment of the present invention includes: overlapping the first steel plate 11 and the second steel plate 12 in the plate thickness direction in such a manner that the end of the first steel plate 11 is arranged on the surface of the second steel plate 12; and arc welding the end 111 of the overlapped first steel plate 11 and the surface 121 of the second steel plate 12 to form a weld bead 13, the surface 121 of the second steel plate 12 having a zinc coating 14, and the arc welding is to periodically move the welding torch A in a direction transverse to the welding direction WD. In the oscillating arc welding with linear swing, the thickness tL (mm) of the second steel plate 12 and the wavelength y (mm) of the waveform of the welding torch A in the oscillating arc welding are set to values ​​satisfying y / tL≤2.8, the width w (mm) of the weld bead 13 and the thickness tL of the second steel plate 12 are set to values ​​satisfying 3.3≤w / tL≤7.0, and the droplet transfer frequency D (times / second) from the welding torch A to the molten pool 13P and the oscillation frequency f (Hz) in the oscillating arc welding are set to values ​​satisfying D / f≥25. Alternatively, a method for manufacturing an arc welded joint according to one embodiment of the present invention includes a step of arc welding the end face of the overlapped first steel plate and the surface of the second steel plate to form a weld bead, the surface of the second steel plate to be arc welded has a zinc coating, the arc welding is oscillating arc welding, the plate thickness tL (mm) of the second steel plate and the wavelength y (mm) of the waveform of the welding torch A in the oscillating arc welding are set to values ​​satisfying y / tL≤2.8, the width w (mm) of the weld bead and the plate thickness tL of the second steel plate are set to values ​​satisfying 3.3≤w / tL≤7.0, and the droplet transfer frequency D (times / second) from the welding torch to the molten pool in the oscillating arc welding and the oscillation frequency f (Hz) are set to values ​​satisfying D / f≥25. The manufacturing method is described in detail below. In addition, the definitions of terms in the manufacturing method of the arc welded joint shown below also apply to the terms in the arc welded joint.

[0043] The present inventors have conducted intensive research on a method for reducing the porosity defects pd in the weld bead 13 obtained by arc welding of a galvanized steel sheet. The present inventors have found that the amount of the porosity defects pd can be drastically reduced by:

[0044] (1) performing oscillatory arc welding under specified conditions by causing the welding torch A to periodically oscillate in a direction transverse to the welding direction WD, and

[0045] (2) The frequency D of droplet transfer from the welding torch A to the molten pool 13P during arc welding is controlled within a prescribed range.

[0046] The oscillating welding method refers to a welding technique in which a weld bead 13 is formed while the welding torch A for arc welding is periodically oscillated in a direction transverse to the welding direction WD. The welding direction WD refers to the extension direction of the weld bead 13 obtained by welding. Oscillating welding arc welding refers to arc welding performed according to the oscillating welding method. An example of a typical trajectory of oscillating welding arc welding is a sine wave. In this case, the moving speed of the welding torch along the welding direction WD is constant, and the welding torch performs simple harmonic vibration in a direction perpendicular to WD. On the other hand, various trajectories can be formed by periodically changing the speed of the welding torch along the welding direction WD and the speed in the direction perpendicular to WD.

[0047] In general, the oscillating welding bead obtained by the oscillating welding method in which the welding torch A is periodically oscillated in a direction transverse to the welding direction WD tends to have a width wider than that of a normal welding bead. For example, in the oscillating welding bead, the ratio of the penetration width to the penetration depth is often greater than that of a normal welding bead. Therefore, when the galvanized steel sheet is subjected to oscillating arc welding, the amount of the zinc coating 14 introduced into the molten pool 13P is greater than that of a normal arc welding. Therefore, from the viewpoint of suppressing the porosity defect pd caused by the zinc coating 14, oscillating arc welding has been considered undesirable in the past. In the welding method disclosed in Patent Document 1, although the tungsten inert gas (TIG) arc is oscillated, at the same time, a gap is provided at the corner to discharge zinc vapor from the molten metal.

[0048] However, the present inventors have found that the amount of porosity defects pd can be drastically reduced by (1) performing oscillating arc welding under predetermined conditions and (2) increasing the droplet transfer frequency D from the welding torch A to the molten pool 13P. The droplet transfer frequency D refers to the frequency of occurrence of a phenomenon in which a droplet d crosses the arc generating portion and transfers from the front end of the welding wire AW to the molten pool 13P. The droplet d refers to a droplet of molten metal formed by melting the welding wire AW by heat such as an arc. It is presumed that since the droplets d frequently fall on the molten metal, the molten metal in the molten pool 13P is stirred, further promoting the discharge of zinc vapor 14v from the molten pool 13P.

[0049] In addition, the inventors have found that although lateral oscillation is necessary to stir the molten pool 13P, it is not preferable that the oscillation frequency in lateral oscillation arc welding is too large. Therefore, (3) it is necessary to make the droplet transfer frequency D and the oscillation frequency f in lateral oscillation arc welding satisfy D / f≥25. In addition, the oscillation frequency f of the welding torch A refers to the reciprocal of the length (seconds) of one cycle when the welding torch A is oscillated periodically.

[0050] The reason for specifying D / f is as follows. In order to promote the discharge of zinc vapor from the molten pool, the molten pool needs to be vigorously stirred. At this time, it is necessary to combine the stirring of the molten metal using the droplet d with the horizontal swinging arc welding. Although it is believed that the increase in the droplet transfer frequency D contributes to the discharge of zinc vapor, according to the research of the inventors, even if the droplet transfer frequency D is increased, the porosity defect rate will not be sufficiently reduced without horizontal swinging.

[0051] On the other hand, when welding is performed to satisfy D / f ≥ 25, the porosity defect rate is reduced. This is believed to be because, by performing the horizontal oscillating welding, the molten droplets d are transferred to various parts of the molten pool 13P, and the stirring of the molten pool 13P becomes more intense. Figure 1 As shown in FIG. 1 , it is considered that the trajectory of the welding torch A is not a straight line, but a non-straight trajectory, such as a sine wave shape, is drawn by performing swaying welding, so that the molten droplet d is uniformly transferred to the entire molten pool 13P. In other words, the molten droplet d is transferred not only in the welding direction, but also in the direction transverse to the welding direction. Thus, the molten pool 13P is stirred not only in the welding direction, but also in the width direction, which can effectively reduce the porosity defect rate.

[0052] However, when the oscillation frequency f is relatively large relative to the droplet transfer frequency D and does not satisfy D / f≥25, the porosity defect rate cannot be sufficiently reduced. It can be considered that this means that if the transition of the droplet d is not continuously performed to a certain extent or more along the oscillating trajectory of the welding torch A during oscillating welding, that is, if the droplets d are not transferred at excessive intervals, the molten pool 13P cannot be sufficiently stirred. The above formula means that the number of droplets d that transition in each cycle of the oscillation of the welding torch A is 25 or more. Furthermore, if the oscillation frequency f is too large, the arc welding may sometimes become unstable. Based on the above reasons, in order to reduce the porosity defect rate of the arc welding joint 1, it is also necessary to satisfy D / f≥25.

[0053] Hereinafter, a method for manufacturing the arc welding joint 1 according to the present embodiment obtained based on the above technical concept will be described in detail.

[0054] In the manufacturing method of the arc welded joint 1 of the present embodiment, first, the first steel plate 11 and the second steel plate 12 are overlapped in the plate thickness direction so that the end 111 of the first steel plate 11 is arranged on the surface 121 of the second steel plate 12. Next, the end 111 of the first steel plate 11 and the surface 121 of the second steel plate 12 are arc welded to form a weld bead 13. During the arc welding, the first steel plate 11 and the second steel plate 12 are overlapped. In addition, the weld bead 13 is formed so as to join the end 111 of the first steel plate 11 and the surface 121 of the second steel plate 12. Therefore, the arc welded joint 1 obtained by the manufacturing method of the present embodiment is a so-called lap fillet weld joint.

[0055] The term "steel plate" is a concept that includes not only plate-shaped members but also plate-shaped portions of members having a three-dimensional shape. For example, a flange portion of a hat-shaped member is also considered a steel plate in the present embodiment.

[0056] At least the surface 121 of the second steel plate 12 overlapping with the first steel plate 11 (i.e., the surface 121 to be arc welded) of the first steel plate 11 and the second steel plate 12 has a zinc-based coating 14. As a result, the corrosion resistance of the arc welded joint 1 is improved. More preferably, both surfaces of the second steel plate 12 have a zinc-based coating 14. More preferably, one or both surfaces of the first steel plate 11 also have a zinc-based coating 14. In addition, the zinc-based coating 14 refers to a coating composed mainly of zinc and further composed of elements such as Si, Al, Mg, and Fe depending on the situation. "The zinc-based coating has a composition mainly composed of zinc" means that the element most contained in the zinc-based coating is zinc. Alternatively, "the zinc-based coating has a composition mainly composed of zinc" means that the Zn content in the zinc-based coating is 50% by mass or more.

[0057] The plating process includes electroplating and hot-dip plating, and sometimes the steel plate and the plating layer are alloyed by heat treatment after plating. The above-mentioned examples of zinc-based plating 14 all have a chemical corrosion protection effect. The composition of the zinc-based plating 14 is determined by the following method. First, an acid containing an inhibitor that inhibits steel corrosion is used to obtain an acid solution that peels off and dissolves the plating. Then, the obtained acid solution is subjected to ICP analysis. In this way, the composition of the zinc-based plating 14 can be determined. Regarding the type of acid, there is no particular limitation as long as it is an acid that can dissolve the zinc-based plating 14. In addition, the composition determined by the above method is the average composition of the entire plating.

[0058] Since the zinc-based coating 14 is disposed on the arc-welded surface 121 of the second steel plate 12, a large amount of zinc is mixed into the molten pool 13P formed by arc welding. Zinc has a lower melting point and boiling point than iron, so during arc welding, the zinc in the molten pool 13P evaporates and becomes zinc vapor 14v. If the molten pool 13P solidifies while the zinc vapor 14v remains in the molten pool 13P, a porosity defect pd is generated in the weld bead 13. In addition, the molten pool 13P refers to a pool of molten metal formed by heat such as an arc during welding. In order to solve this problem, in the arc welding head 1 of the present embodiment, the swaying wire running condition and the droplet transfer frequency D are specified as described below.

[0059] (1. Horizontal swaying conditions)

[0060] The arc welding is oscillating arc welding. In oscillating arc welding, the welding torch A is periodically oscillated in a direction transverse to the welding direction WD. The oscillating arc welding is performed in a manner that satisfies the following equations 1 and 2.

[0061]

Formula 1

[0062]

[0063] 3.3≤w / tL≤7.0(Formula 2)

[0064] Here, the symbols included in the above formula are defined as follows.

[0065] y: wavelength of the waveform of the welding torch A in oscillating arc welding (i.e., the trajectory formed by the periodic oscillation of the welding torch A) (mm)

[0066] In other words, y is the distance that the periodically oscillating welding torch A moves along the welding direction WD in each cycle.

[0067] tL: Thickness of the second steel plate 12 (mm)

[0068] v: Moving speed of welding torch A along welding direction WD (m / min)

[0069] f: Oscillation frequency of welding torch A (Hz)

[0070] w: width of weld bead 13 (mm)

[0071] The coefficient "50 / 3" (i.e., "1000 / 60") included in Formula 1 is used to set the unit of the torch moving speed v to "m / min" and the unit of the oscillation frequency f to "Hz" (i.e., "sec -1 ”), and the value matching the unit “mm” of the wavelength y of the waveform.

[0072] The values ​​corresponding to these symbols are described in more detail as follows.

[0073] As described above, in the oscillating arc welding, the welding torch A for arc welding is periodically oscillated in a direction transverse to the welding direction WD, while the weld bead 13 is formed. In the oscillating arc welding in which the welding torch A is periodically oscillated, the wavelength y of the waveform of the welding torch A refers to the moving distance of the welding torch A during one cycle of the oscillating arc welding along the welding direction WD. Figure 1 An example of the waveform wavelength y is shown in FIG. The waveform wavelength y is the moving distance measured along the welding direction WD. Figure 1 The moving distance of the welding torch (shown by the dotted line) and the wavelength y of the waveform of the welding torch are different concepts.

[0074] The moving speed v of the welding torch A along the welding direction WD is a value obtained by dividing the moving distance of the welding torch A along the welding direction WD by the time required for the movement. The moving speed in the transverse direction to the welding direction WD is not included in v.

[0075] The oscillation frequency f of the welding torch A is the reciprocal of the length (seconds) of one cycle when the welding torch A is oscillated periodically.

[0076] The width w of the weld bead 13 refers to the length (width) of the weld bead 13 measured along the welding direction WD, that is, the direction perpendicular to the extending direction of the weld bead 13 .

[0077] The plate thickness tL of the second steel plate 12 refers to the plate thickness tL of the second steel plate at the welded portion and its vicinity. When the plate thickness tL of the second steel plate is non-uniform, the plate thickness of the second steel plate at the welded portion and its vicinity is regarded as tL. Regarding the plate thickness, the average value measured at at least two locations within a range of 10 mm from the weld toe of the weld bead in a direction perpendicular to the extending direction of the weld bead is regarded as the plate thickness tL of the second steel plate 12. The plate thickness can be measured by a micrometer, a vernier caliper, etc., or by observing a cross section collected after cutting with a microscope.

[0078] As shown in Formula 1, the wavelength y of the waveform of the welding torch A is a function of the moving speed v of the welding torch A and the oscillation frequency f of the welding torch A. In addition, the inventors determined the upper limit of the wavelength y of the waveform of the welding torch A based on the thickness tL of the second steel plate 12. The thicker the second steel plate 12 (equivalent to the so-called "lower plate" in the lap fillet weld joint), the greater the input heat required in the arc welding. In general arc welding, the input heat is set to a level that can ensure a penetration depth of about 1 / 2 of the thickness of the lower plate. The larger the thickness tL of the lower plate, the greater the required input heat, and the more zinc vapor 14v is generated. Therefore, when determining the wavelength y of the waveform used to suppress the zinc vapor 14v, the thickness tL of the lower plate is also considered.

[0079] If y / tL exceeds 2.8, the molten pool 13P is solidified before the zinc vapor 14v is discharged outside the molten pool 13P, and there is a high possibility that a porosity defect pd will occur in the weld bead 13. Therefore, y / tL is set to 2.8 or less. y / tL is preferably 2.6 or less, 2.4 or less, or 2.0 or less.

[0080] The lower limit of y is not particularly limited. From the viewpoint of promoting the discharge of zinc vapor 14v from the molten pool 13P and reducing the porosity defects pd of the weld bead 13, the smaller y is, the more preferable. However, the smaller y is, the slower the moving speed v of the welding torch A is, and the lower the welding efficiency is. In addition, the smaller y is, the greater the oscillation frequency f of the welding torch A is, and the arc welding sometimes becomes unstable. Moreover, by increasing the wavelength y of the waveform of the welding torch A, the weld bead 13 is formed into a waveform, so that the fatigue strength improvement effect described later can be obtained. From the viewpoint of ensuring welding efficiency and welding stability, y / tL can also be set to 0.7 or more.

[0081] In addition, the wavelength y of the waveform of the welding torch A during yaw arc welding often matches the wavelength of the waveform of the weld toe 1311 formed at the stable portion 131 of the weld bead 13. However, it is sometimes difficult to determine the wavelength of the waveform of the weld toe 1311 of the stable portion 131 of the weld bead 13. In this case, it is difficult to determine the wavelength y of the waveform of the welding torch A based on the analysis of the weld bead 13. In particular, when the wavelength y of the waveform of the welding torch A is short and the weld toe 1311 of the stable portion 131 of the weld bead 13 does not have a wavy shape, a direct trace of the waveform of the welding torch A does not remain on the weld bead 13.

[0082] In addition, as shown in Formula 2, the upper and lower limits of the width w of the weld bead 13 are determined according to the plate thickness tL of the second steel plate 12. When w / tL is too small, the molten pool 13P is not sufficiently stirred. On the other hand, when w / tL is too large, the molten pool 13P solidifies before the molten pool 13P is stirred. In either case, the zinc vapor 14v cannot be sufficiently discharged from the molten pool 13P. Therefore, w / tL is set to be greater than 3.3 and less than 7.0. w / tL may also be set to be greater than 3.5, greater than 4.0, or greater than 4.5. w / tL may also be set to be less than 6.5, less than 6.0, or less than 5.5.

[0083] In addition, there is a good correlation between the width w (mm) of the weld bead 13 and the swing amplitude x (mm) of the welding torch A. Figure 1 As shown in FIG. 1 , the oscillation amplitude x of the welding torch A in the oscillating arc welding in which the welding torch A for arc welding is periodically moved in the lateral direction relative to the welding direction WD is a value that is half the width of the moving range of the welding torch A during one cycle. The "width" refers to the width measured in a direction perpendicular to the welding direction WD. In addition, the width w of the weld bead 13 is affected by the current value, voltage value, welding speed (i.e., the moving speed v of the welding torch A along the welding direction WD) and the composition of the molten pool 13P in addition to the oscillation amplitude x of the welding torch A. By appropriately controlling these matters, a weld bead 13 having a width close to the target value can be produced.

[0084] (2. Droplet transfer frequency)

[0085] In arc welding, it is also necessary to set the droplet transfer frequency D (times / second) from the welding torch A to the molten pool 13P and the oscillation frequency f to values ​​satisfying D / f≥25. The droplets d dripping into the molten pool 13P have the effect of stirring the molten pool 13P and further promoting the discharge of zinc vapor 14v from the molten pool 13P. However, when D / f is less than 25, this effect cannot be fully obtained. Therefore, D / f is set to be greater than 25. D / f can also be set to be greater than 27, greater than 30, or greater than 35. The upper limit value of D / f is not particularly limited, for example, it can also be set to be less than 55, less than 50, or less than 48.

[0086] By setting the arc welding to pulse arc welding, the droplet transfer frequency D can be controlled. Pulse arc welding refers to arc welding performed by periodically increasing and decreasing the current so that the current waveform is pulsed. There is a correlation between the pulse frequency and the droplet transfer frequency D. Generally, the higher the pulse frequency, the higher the droplet transfer frequency D. In addition, the droplet transfer frequency D is also affected by the feed speed of the welding wire AW, the shielding gas composition, and the current value. By measuring the droplet transfer frequency D while appropriately changing these welding conditions, the welding conditions for obtaining the desired droplet transfer frequency D can be determined.

[0087] By observing the molten pool 13P with a high-speed camera, the droplet transfer frequency D can be measured. However, after the molten pool 13P solidifies, no direct trace of the droplet transfer frequency D remains on the weld bead 13. Therefore, it is necessary to measure the droplet transfer frequency D during the arc welding process. However, it is not necessary to always measure the droplet transfer frequency D during the arc welding process. If the above-mentioned welding conditions that affect the droplet transfer frequency D are constant, the droplet transfer frequency D is also substantially constant. Therefore, in the swaying arc welding performed under the condition that it is confirmed in advance that the specified droplet transfer frequency D can be achieved, it is considered that the droplet transfer frequency D is set to the specified value.

[0088] (Si content of weld bead 13)

[0089] In the method for manufacturing the arc welding joint 1 of the present embodiment, it is further preferred that the Si content of the weld bead 13 is set to 0.5 mass % or less. The inventors have found that by reducing the Si content of the molten pool 13P, the porosity defects pd contained in the weld bead 13 formed by solidifying the molten pool 13P are further reduced. Although the reason is not clear at present, it is speculated that if the Si content of the molten pool 13P is reduced, the viscosity of the molten pool 13P is reduced, and the discharge of zinc vapor 14v from the molten pool 13P is further promoted. This effect is significantly exhibited when the Si content of the weld bead 13 obtained after arc welding is 0.5 mass % or less. The Si content of the weld bead 13 may also be set to 0.4 mass % or less, 0.3 mass % or less, or 0.2 mass % or less.

[0090] The Si content of the weld bead 13 can be determined by cutting the vicinity of the apex of the weld bead 13 and measuring the composition of the cut powder using a known analysis method such as ICP. The Si content of the weld bead 13 is affected by the Si content of the first steel plate 11 and the second steel plate 12, the Si content of the welding wire, and the mixing ratio of the base material component and the welding wire component. Therefore, the Si content of the weld bead 13 can be controlled by selecting the welding wire component suitable for the composition of the steel plate to be welded and the mixing ratio of the base material component and the welding wire component.

[0091] (Preferred lower limit value of wavelength y of the waveform of the welding torch)

[0092] When the wavelength y of the waveform of the welding torch A during oscillating arc welding is large, the weld toe 1311 of the stable portion 131 of the weld bead 13 has a wavy shape reflecting the oscillating arc welding of the welding torch A. The weld toe 1311 refers to a line where the surface of the base material and the surface of the weld bead 13 intersect. On the other hand, when the wavelength y of the waveform of the welding torch A is small, no wavy shape is confirmed at the weld toe 1311. In conventional oscillating arc welding, from the viewpoint of adjusting the shape of the weld bead 13 to improve the appearance, the wavy shape is often not provided at the weld toe 1311 by reducing the wavelength y. However, the inventors have found that the fatigue strength of the arc welding joint 1 is improved by making the shape of the weld toe 1311 on the second steel plate 12 side wavy. The inventors speculate that the reason for this is that the stress applied to the weld bead 13 is well dispersed by making the shape of the weld toe 1311 wavy.

[0093] (Prevention of melt-through)

[0094] The higher the input heat in arc welding, the deeper the molten pool 13P. As a result, the molten pool 13P sometimes penetrates the second steel plate 12 and the weld bead 13 is exposed on the back side of the second steel plate 12. This phenomenon is generally called "penetration". If penetration occurs, the molten metal constituting the molten pool 13P drips, so the welding workability is impaired. In addition, in the case where both surfaces of the second steel plate 12 have a zinc-based coating 14, the zinc-based coating 14 on the back side of the second steel plate 12 is mixed into the molten pool 13P due to penetration. As a result, the amount of zinc vapor 14v increases, and the porosity defect pd increases.

[0095] Therefore, in the method for manufacturing the arc welded joint 1 of the present embodiment, it is preferred that the weld bead 13 does not penetrate the second steel plate 12 in the plate thickness direction. That is, in the method for manufacturing the arc welded joint 1 of the present embodiment, it is preferred that the surface of the second steel plate 12 on the opposite side to the surface 121 to be arc welded is not melted during arc welding. In other words, it is preferred that the back surface of the second steel plate 12 is maintained in a solid state during arc welding. Thus, the amount of porosity defects pd can be further reduced. By reducing the input heat during arc welding and reducing the penetration depth of the weld bead 13, it is possible to prevent penetration.

[0096] (Ensure the penetration depth)

[0097] On the other hand, from the viewpoint of stably ensuring the joint strength of the arc welded joint 1, it is preferable to increase the penetration depth of the weld bead 13. For example, in the method for manufacturing the arc welded joint 1 of the present embodiment, it is preferable that the outer edge of the weld bead 13 intersects with the butt surface of the first steel plate and the second steel plate in the cross section along the plate thickness direction. That is, in the method for manufacturing the arc welded joint 1 of the present embodiment, Figure 2As shown, the root R may be melted during arc welding to grow the weld bead to the butting surface between the first steel plate and the second steel plate.

[0098] The root R refers to the bottom portion to be welded, specifically, the portion where the end surface of the first steel plate 11 intersects with the arc-welded surface 121 of the second steel plate 12. The outer edge of the weld bead 13 refers to the surface of the weld bead 13 and the molten boundary (the boundary between the weld bead 13 and the base material). By etching the cross section of the arc welded joint 1, the molten boundary can be easily visually identified.

[0099] When the penetration depth is shallow and the molten pool 13P does not reach the root R, Fig. 8A As shown in the example, a gap C is formed near the root R, that is, at the corner of the joint. On the other hand, by forming the molten pool 13P to reach the root R, the penetration depth of the weld bead 13 can be increased, as shown in FIG. Figure 8B By making the joint corner portion solid as shown in the example, the joining strength of the arc welding joint 1 can be stably ensured.

[0100] (Oscillation frequency f)

[0101] In the manufacturing method of the arc welding joint 1 of the present embodiment, it is preferable that the oscillation frequency f of the oscillating arc welding is less than 10 Hz. By making the oscillation frequency f less than 10 Hz, the stability of the arc welding can be further improved. The oscillation frequency f can also be set to 9 Hz or less, 8 Hz or less, or 7 Hz or less.

[0102] (Types of Arc Welding)

[0103] Arc welding is preferably Metal Active Gas (MAG) welding. Tungsten Inert Gas (TIG) welding and plasma arc welding described in Patent Document 1 in arc welding are non-consumable electrode welding, and therefore cannot achieve stirring of the molten pool by combining swaying and droplet transfer. Metal Inert Gas (MIG) welding is different from Metal Active Gas (MAG) welding in that the shielding gas uses an inactive gas mainly composed of argon or helium, but the gas is relatively expensive. In addition, since the arc tends to expand, sufficient penetration may not be achieved in some cases. On the other hand, Metal Active Gas (MAG) welding does not have these disadvantages.

[0104] Next, another embodiment of the arc welding joint 1 of the present invention is described. The arc welding joint 1 of the present embodiment includes: a first steel plate portion 21; a second steel plate portion 22 overlapping the first steel plate portion 21 in the plate thickness direction; and a weld bead 13, which joins the end of the first steel plate portion 21 disposed on the surface 121 of the second steel plate portion 22 to the surface 121 of the second steel plate portion 22, a zinc-based coating 14 is present in a region of the surface 121 of the second steel plate portion 22 where the weld bead 13 is not provided, a width w of the weld bead 13 and a plate thickness tL of the second steel plate portion 22 satisfy 3.3≤w / tL≤7.0, and a porosity defect rate of a stable portion 131 of the weld bead 13 is less than 10%. That is, the arc welding joint of the present embodiment comprises: a first steel plate; a second steel plate overlapping the first steel plate; and a weld bead extending linearly along the end of the first steel plate to join the end of the first steel plate to the surface of the second steel plate, the second steel plate having a zinc coating on the surface provided with the weld bead, the width w of the weld bead and the plate thickness tL of the second steel plate satisfy 3.3≤w / tL≤7.0, and the porosity defect rate of the stable portion of the weld bead is less than 10%. Hereinafter, each component of the arc welding joint 1 of the present embodiment will be described in detail.

[0105] The arc welding head 1 of the present embodiment includes a first steel plate portion 21 and a second steel plate portion 22 overlapping the first steel plate portion 21. The first steel plate portion 21 is the first steel plate 11 after welding. The second steel plate portion 22 is the second steel plate 12 after welding. In order to distinguish between an object before welding and an object after welding, in the present embodiment, a steel plate as a component of a welded joint is referred to as a "steel plate portion", and a steel plate as a raw material of a welded joint is referred to as a "steel plate".

[0106] In addition, similar to the above-mentioned “steel plate”, the “steel component” is also a concept that includes not only a plate-shaped component but also a plate-shaped portion of a component having a three-dimensional shape. For example, the flange portion of a hat-shaped component is also regarded as a steel component in this embodiment. Other preferred embodiments of the above-mentioned first steel plate 11 and second steel plate 12 can also be applied to the first steel plate portion 21 and second steel plate portion 22.

[0107] Furthermore, the arc welding joint 1 of the present embodiment has a weld bead 13 that joins the end of the first steel plate portion 21 disposed on the surface 121 of the second steel plate portion 22 to the surface 121 of the second steel plate portion 22. The weld bead joins the end of the first steel plate portion 21 to the surface 121 of the second steel plate portion 22 along the end of the first steel plate portion 21. Therefore, the arc welding joint 1 of the present embodiment is a so-called lap fillet weld joint.

[0108] There is a zinc-based coating 14 on the surface 121 of the second steel plate portion 22. That is, a portion or all of the surface 121 of at least the second steel plate portion 22 where the weld bead 13 is arranged, of the first steel plate portion 21 and the second steel plate portion 22, has the zinc-based coating 14. Thus, the corrosion resistance of the arc welding joint 1 is improved. However, there is no zinc-based coating 14 in the region where the weld bead 13 is not provided. That is, the zinc-based coating 14 is in the region where the weld bead 13 is not provided on the surface of the second steel plate portion 22. It is more preferred that the zinc-based coating 14 is provided on both surfaces of the second steel plate portion 22. It is further preferred that the surface of one or both of the first steel plate portion 21 also has the zinc-based coating 14.

[0109] (Weld bead width w and porosity defect rate)

[0110] In the arc welding joint 1 of the present embodiment, the width w of the weld bead 13 and the plate thickness tL of the second steel plate portion 22 satisfy 3.3≤w / tL≤7.0, and the porosity defect rate of the stabilizing portion 131 of the weld bead 13 is less than 10%. Such a weld bead 13 can be manufactured by arc welding as follows, for example, as in the manufacturing method of the arc welding joint 1 of the present embodiment described above:

[0111] (1) Perform horizontal arc welding under specified conditions, and

[0112] (2) The frequency D of droplet transfer from the welding torch A used for arc welding to the molten pool 13P is set within a predetermined range.

[0113] By making the porosity defect ratio less than 10%, the joining strength of the arc welding joint 1 can be improved, and the electrodeposition coating defects can be suppressed.

[0114] In addition, the stable portion 131 of the weld bead 13 refers to the area other than the starting end portion 132 and the terminal end portion 133 of the weld bead 13. Figure 5 As shown in the image of FIG. 1 , the starting end 132 and the terminal end 133 of the weld bead 13 are formed in an unstable welding arc state, so their width and shape are uneven. In the arc welding head 1 of the present embodiment, the area within 15 mm from the starting end of the weld bead 13 is defined as the starting end 132, the area within 15 mm from the terminal end is defined as the terminal end 133, and the area other than this is defined as the stable portion 131.

[0115] The porosity defect rate of the stable portion 131 of the weld bead 13 is measured by the following steps. First, an X-ray transmission image of the stable portion 131 of the weld bead 13 is captured. Thus, the porosity defects pd included in the weld bead 13 can be confirmed. Next, the total value of the lengths of the porosity defects pd along the weld bead 13 is measured. Then, the total value of the lengths of the porosity defects pd is divided by the length of the stable portion 131, thereby calculating the porosity defect rate.

[0116] In order to illustrate the method of measuring the porosity defect rate, Figure 5 FIG. 1 shows an X-ray transmission image of the weld bead 13 with a porosity defect rate of 0% in the stabilizing portion 131. Figure 6 FIG. 1 shows an X-ray transmission image of the weld bead 13 having a porosity defect rate of 52.0% in the stabilizing portion 131. Figure 5 In the image of , since the porosity defects pd are not confirmed at all, the total length of the porosity defects pd along the weld bead 13 is regarded as 0 mm. Figure 6 In the image, a large number of porosity defects pd are confirmed in weld bead 13. Figure 6 An image in which these porosity defects pd are projected onto a line along the weld bead 13 is shown on the weld bead 13. The total value of the projected line is the total value of the length of the porosity defects pd along the weld bead 13.

[0117] (Si content of weld bead 13)

[0118] In the arc welding head 1 of the present embodiment, it is further preferred that the Si content of the weld bead 13 is set to 0.5 mass % or less. Thus, the porosity defect pd is further reduced. The Si content of the weld bead 13 may be set to 0.4 mass % or less, 0.3 mass % or less, or 0.2 mass % or less. The Si content of the weld bead 13 can be measured by the above method.

[0119] (Shape of Weld Toe 1311 on the Second Steel Plate Part 22 Side in Stabilizing Part 131 of Weld Bead 13)

[0120] like Figure 7 As shown, in the stable portion 131 of the weld bead 13, the weld toe 1311 on the second steel plate portion 22 side may also have a wavy shape. Here, the wavy shape refers to a shape in which concave portions and convex portions appear alternately and periodically. In addition, the wavelength Y of the weld toe 1311 and the plate thickness tL of the second steel plate portion 22 may also satisfy 0.7≤Y / tL≤2.8.

[0121] In conventional swaying arc welding, from the viewpoint of adjusting the shape of the weld bead 13 and improving the appearance, the wavelength y of the waveform of the welding torch is reduced and the wavy shape is not provided at the weld toe 1311 in many cases. In the arc welding joint 1 of the present embodiment, from the viewpoint of suppressing the porosity defect, it is also not necessary to provide the wavy shape at the weld toe 1311. However, the inventors have found that the fatigue strength of the arc welding joint 1 is improved by making the shape of the weld toe 1311 on the second steel plate portion 22 side wavy. The inventors presume that the reason for this is that the stress applied to the weld bead 13 is well dispersed by making the shape of the weld toe 1311 wavy.

[0122] However, the smaller the wavelength Y of the weld toe, the more difficult it is to visually recognize the wavy shape of the weld toe, and the more difficult it is to obtain the effect of improving fatigue strength. From the viewpoint of ensuring the effect of improving fatigue strength, it is preferably set to 0.7≤Y / t. On the other hand, by setting Y / tL≤2.8, the generation of the porosity defect pd in the weld bead 13 can be effectively suppressed. Therefore, the wavelength Y of the weld toe 1311 on the second steel plate part 22 side in the stable part 131 of the weld bead 13 and the plate thickness tL of the second steel plate part 22 can also satisfy Y / tL≤2.8.

[0123] However, as described above, from the viewpoint of reducing the porosity defects, the wavelength y in the oscillating arc welding may be reduced so that the weld toe 1311 is smooth to the extent that the wavy shape cannot be confirmed. In addition, even when the wavy shape is not confirmed in the weld toe 1311 of the weld bead 13, when the ratio between the width of the weld bead 13 in the stable portion and the penetration depth of the weld bead 13 measured in the cross section perpendicular to the extension direction of the weld bead 13 (weld bead width ÷ penetration depth) exceeds 10, it is estimated that the weld bead 13 is formed by oscillating arc welding. The penetration depth refers to the maximum value of the depth of the weld bead 13 measured in the cross section from the surface 121 of the second steel plate portion 22 as a reference.

[0124] (Prevention of melt-through)

[0125] If the input heat in arc welding is high, penetration may occur. If penetration occurs, the molten metal constituting the molten pool 13P drips, thereby impairing welding workability. In addition, in the case where the surfaces of both sides of the second steel plate portion 22 have the zinc-based coating 14, the zinc-based coating 14 on the back side of the second steel plate portion 22 is mixed into the molten pool 13P due to penetration. As a result, the amount of zinc vapor 14v increases, and the porosity defect pd increases. Therefore, in the arc welding joint 1 of the present embodiment, it is preferred that the weld bead 13 does not penetrate the second steel plate portion 22 in the plate thickness direction. That is, in the arc welding joint 1 of the present embodiment, it is preferred that the weld bead 13 does not expose on the surface of the second steel plate portion 22 on the opposite side of the surface 121 on which the weld bead 13 is provided. As a result, the amount of the porosity defect pd can be further reduced.

[0126] (Ensure the penetration depth)

[0127] On the other hand, from the viewpoint of stably ensuring the joining strength of the arc welding joint 1, it is preferable to increase the penetration depth of the weld bead 13. Figure 8BAs shown, in the arc welding joint 1 of the present embodiment, in the cross section along the plate thickness direction, the root R, which is the portion where the end surface of the first steel plate portion 21 and the surface of the second steel plate portion 22 intersect, may also be included in the weld bead 13. In other words, in the cross section of the arc welding joint 1 along the extending direction of the weld bead 13, the outer edge of the weld bead 13 may also intersect with the butt surface of the first steel plate portion 21 and the second steel plate portion 22. By making the weld bead 13 grow beyond the root R, the butt surface of the first steel plate portion 21 and the second steel plate portion 22 intersects with the outer edge of the weld bead 13, thereby increasing the penetration depth of the weld bead 13 and stably ensuring the joining strength of the arc welding joint 1.

[0128] (Other preferred methods)

[0129] In the manufacturing method of the arc welding joint 1 and the arc welding joint 1 of the present embodiment, various modes other than the above can be appropriately adopted. A more preferred mode is exemplified below. Unless otherwise specified, the modes exemplified below can be applied to both the manufacturing method of the arc welding joint 1 and the arc welding joint 1 of the present embodiment. The preferred modes of the first steel plate 11 and the second steel plate 12 as raw materials of the arc welding joint can also be applied to the first steel plate portion 21 and the second steel plate portion 22 as components of the arc welding joint.

[0130] The thickness of the first steel plate 11 is not particularly limited. For example, when the first steel plate 11 is a steel plate for automobiles, the thickness of the first steel plate 11 is preferably 0.8 mm or more and 4.0 mm or less. Similarly, the thickness tL of the second steel plate 12 is not particularly limited. When it is a steel plate for automobiles, the thickness is preferably 0.8 mm or more and 4.0 mm or less.

[0131] The tensile strength of the first steel plate 11 is not particularly limited. For example, the tensile strength of the first steel plate 11 can be set to 440 MPa or more and 1500 MPa or less. Similarly, the tensile strength of the second steel plate 12 is not particularly limited. For example, the tensile strength of the second steel plate 12 can be set to 440 MPa or more and 1500 MPa or less. The chemical composition and metal structure of these steel plates are not particularly limited, and a known preferred structure can be appropriately adopted.

[0132] The thickness and composition of the zinc-based plating layer 14 are not particularly limited. The amount of the zinc-based plating layer 14 deposited can be, for example, 5 g / m 2 Above and 200g / m 2 Here, the coating amount of the zinc-based plating layer 14 refers to the total amount of zinc and other elements contained in the zinc-based plating layer 14. Examples of elements other than zinc contained in the zinc-based plating layer 14 include Si, Al, Mg, and Fe.

[0133] Alternatively, only the amount of zinc contained in the zinc-based plating layer 14 may be separately specified. For example, the zinc content per single surface of the zinc-based plating layer 14 may be set to 20 g / m 2 The zinc content per single side of the zinc-based coating 14 does not include the amount of alloy elements other than zinc, such as Si, Al, Mg, and Fe. In addition, the amount of adhesion per single side refers to the amount of adhesion of the zinc-based coating 14 disposed only on the surface of the first steel sheet 11 side of the two surfaces of the second steel sheet 12.

[0134] In addition, in the arc welding head 1 of the present embodiment, the zinc-based plating layer 14 may be present within 100 μm near the weld bead 13. That is, the interval between the zinc-based plating layer 14 and the weld bead 13 is preferably 100 μm or less. As a result, the corrosion resistance near the weld bead 13 is further improved. The interval between the zinc-based plating layer 14 and the weld bead 13 is preferably as small as possible, and may be 0 μm. That is, the zinc-based plating layer 14 and the weld bead 13 may also be in contact.

[0135] In the method for manufacturing the arc welding joint 1 of the present embodiment, it is not necessary to remove the zinc-based plating from the surface 121 of the second steel plate 12 before arc welding. During arc welding, the zinc-based plating 14 may evaporate near the weld bead 13, thereby generating a gap between the weld bead 13 and the zinc-based plating 14. However, by performing arc welding without removing the zinc-based plating 14 from the surface 121 of the second steel plate 12, the gap between the zinc-based plating 14 and the weld bead 13 can be easily made 100 μm or less. If the zinc-based plating 14 is removed from the surface 121 of the second steel plate 12 before arc welding, the gap between the weld bead 13 and the zinc-based plating 14 may exceed 100 μm at a part or all of the weld toe of the weld bead 13.

[0136] In addition, the zinc-based plating layer 14 only needs to be disposed on at least the arc-welded surface 121 of the second steel plate 12. Therefore, a plating layer different from the zinc-based plating layer 14 may be provided on the surface of the first steel plate 11 and the surface of the side not arc-welded of the second steel plate 12. Examples of plating layers different from the zinc-based plating layer 14 include aluminum plating layers and the like.

[0137] In addition, the arc welding joint 1 may have a coating film for the purpose of improving corrosion resistance, etc. The coating film is, for example, an electrodeposition coating film. The method for manufacturing the arc welding joint 1 may include a coating step such as an electrodeposition coating step, for example.

[0138] The above-mentioned structure of the manufacturing method of the arc welding joint 1 of the present embodiment only needs to be applied to at least a part of the welding target part of the arc welding joint 1. The above-mentioned structure of the arc welding joint 1 only needs to be applied to at least a part of the welding part of the arc welding joint 1. Preferably, the above-mentioned structure is applied to the entire welding part of the first steel plate 11 and the second steel plate 12. However, for example, in order to improve welding efficiency, the above-mentioned structure may be applied only to the part where the suppression of the porosity defect pd is strongly required, and the structure of the general arc welding joint 1 may be applied to the other parts.

[0139] The trajectory shape of the welding torch A during oscillating arc welding is not particularly limited as long as the above requirements are met. The trajectory of the welding torch A can be, for example, a sine wave shape. For example, by setting the moving speed v of the welding torch A along the welding direction WD to be constant and making the welding torch A perform simple harmonic vibration in a direction perpendicular to the welding direction WD, the trajectory of the welding torch A can be made into a sine wave shape. On the other hand, by periodically changing the moving speed v of the welding torch A along the welding direction WD, the trajectory shape of the welding torch A can be changed in various ways.

[0140] The application of the arc welding joint 1 of the present embodiment is not limited. Examples of preferred applications of the arc welding joint 1 of the present embodiment include building materials and automobile parts.

[0141] Another aspect of the present invention is an automobile component having the arc welding joint 1 of the present embodiment. Therefore, the automobile component of the present embodiment is made of a galvanized steel sheet and has excellent corrosion resistance. In addition, the automobile component of the present embodiment suppresses pore defects and has excellent joint strength and electrodeposition coating properties.

[0142] Example

[0143] The effect of one embodiment of the present invention is described in more detail by way of example. However, the conditions in the example are only a conditional example adopted to confirm the feasibility and effect of the present invention. The present invention is not limited to this conditional example. The present invention may adopt various conditions as long as it does not depart from the gist of the present invention and achieves the purpose of the present invention.

[0144] Arc welded joints were produced under various welding conditions. These arc welded joints were obtained by arc welding the ends of the overlapped first steel plates and the surfaces of the second steel plates to form weld beads.

[0145] Table 1A or Table 1B shows the thickness tL of the second steel plate, the width w of the weld bead, the wavelength y of the waveform of the welding torch, the oscillation amplitude x of the welding torch, the moving speed v of the welding torch along the welding direction, and the oscillation frequency f of the welding torch. In addition, Table 1B also shows the value D / f obtained by dividing the droplet transfer frequency D by the oscillation frequency f of the welding torch. In addition, in some examples, the weld bead is produced by ordinary arc welding instead of oscillating arc welding. In the example where oscillating arc welding is not performed, D / f is recorded as "-". In addition, in the oscillating arc welding device used by the inventor, there is a slight deviation between the set value and the actual value of the oscillation amplitude x of the welding torch. Both the set value and the actual value of the oscillation amplitude x of the device are recorded in Table 1A.

[0146] Table 2 shows the wavelength Y of the weld toe on the second steel sheet side in the stable portion of the weld bead and the Si content of the weld bead obtained by arc welding. For reference, Table 2 also shows the calculated values ​​of y / tL and w / tL. In addition, for some examples, Table 2 also shows the value obtained by dividing the width of the weld bead by the penetration depth of the weld bead. In addition, in the stable portion of the weld bead of some examples, the weld toe on the second steel sheet side does not have a wavy shape. For such examples, Y and Y / tL are recorded as "-".

[0147] Furthermore, the porosity defect rate of the stable portion of the weld bead was measured by X-raying the weld bead of the arc welding joint. Table 2 also shows the porosity defect rate.

[0148]

Table 1A

[0149]

[0150]

Table 1B

[0151]

[0152]

Table 2

[0153]

[0154] In Comparative Example 4, the width w of the weld bead and the thickness tL of the second steel plate do not satisfy the relationship of 3.3≤w / tL≤7.0. Therefore, in Comparative Example 4, the porosity defect rate is not suppressed.

[0155] In Comparative Examples 6 and 7, sway welding was not performed, and the droplet transfer frequency D from the welding torch to the molten pool and the oscillation frequency f did not satisfy the relationship of D / f ≥ 25. Therefore, in Comparative Examples 6 and 7, the porosity defect rate was not suppressed.

[0156] In Comparative Example 10, the droplet transfer frequency D from the welding torch to the molten pool and the oscillation frequency f do not satisfy the relationship of D / f ≥ 25. Therefore, in Comparative Examples 6 and 7, the porosity defect rate is not suppressed.

[0157] In Comparative Example 12, the sway welding was not performed, and the width w of the weld bead and the thickness tL of the second steel plate did not satisfy the relationship of 3.3≤w / tL≤7.0. Therefore, in Comparative Example 12, the porosity defect rate was not suppressed.

[0158] In Comparative Example 13, the wavelength y of the waveform of the welding torch and the plate thickness tL of the second steel plate do not satisfy the relationship of y / tL≤2.8. Therefore, in Comparative Example 13, the porosity defect rate is not suppressed.

[0159] On the other hand, in all the examples where the welding conditions were appropriate, the porosity defect rate was suppressed to less than 10%. In addition, in Example 9, the wavelength y of the waveform of the welding torch was small, so the shape of the weld toe of the weld bead did not become a wavy shape. Therefore, the wavelength Y of the weld toe of Example 9 is recorded as "-" in Table 1B. However, in Example 9, the effect of suppressing porosity defects was also sufficiently obtained. In other examples, the wavelength y of the waveform of the welding torch was substantially consistent with the wavelength Y of the weld toe.

[0160] In addition, in the examples where the Si content of the weld bead was 0.5 mass% or less, the porosity defects were further suppressed. The porosity defect rate of Example 8 where the Si content of the weld bead exceeded 0.5 mass% was 9.3%. On the other hand, the porosity defect rates of Examples 1, 2, 3, 5, 9, and 11 where the Si content of the weld bead was 0.5 mass% or less were all lower than that of Example 8.

[0161] Explanation of symbols

[0162] 1: arc welding joint; 11: first steel plate; 111: end; 12: second steel plate; 121: surface to be arc welded; 13: weld bead; 131: stabilizing portion; 1311: weld toe; 132: starting portion; 133: terminal portion; 13P: molten pool; 14: zinc coating; 14v: zinc vapor; 21: first steel plate portion; 22: second steel plate portion; A: welding torch; AW: welding wire; d: molten droplet; D: molten droplet transition frequency; pd: porosity defect; R: root; C: gap; tL: thickness of second steel plate; WD: welding direction; w: width of weld bead; x: oscillation amplitude of welding torch; y: wavelength of waveform of welding torch.

Claims

1. A method for manufacturing an arc welding joint, comprising: overlapping the first steel plate and the second steel plate in a plate thickness direction in such a manner that an end portion of the first steel plate is disposed on a surface of the second steel plate; and arc welding the end portion of the overlapped first steel plate and the surface of the second steel plate to form a weld bead, The surface of the second steel sheet has a zinc-based plating layer. The above arc welding is a horizontal swing arc welding in which the welding torch is periodically swung in a direction transverse to the welding direction. The thickness tL (mm) of the second steel plate and the wavelength y (mm) of the waveform of the welding torch in the yaw arc welding are set to values ​​satisfying y / tL≤2.

8. The width w (mm) of the weld bead and the thickness tL of the second steel plate are set to values ​​satisfying 3.3≤w / tL≤7.0, The droplet transfer frequency D (times / second) from the welding torch to the molten pool and the oscillation frequency f (Hz) in the oscillating arc welding are set to values ​​satisfying D / f≥25.

2. The method for manufacturing an arc welding joint according to claim 1, characterized in that: The Si content of the weld bead is set to 0.5 mass % or less.

3. The method for manufacturing an arc welding joint according to claim 1 or 2, characterized in that: The wavelength y of the waveform of the welding torch and the plate thickness tL of the second steel plate are set to values ​​satisfying 0.7≤y / tL.

4. The method for manufacturing an arc welding joint according to any one of claims 1 to 3, characterized in that: The weld bead does not penetrate the second steel plate in the plate thickness direction.

5. The method for manufacturing an arc welding joint according to any one of claims 1 to 4, characterized in that: In the cross section along the plate thickness direction, the outer edge of the weld bead intersects with the butt surface between the first steel plate and the second steel plate.

6. The method for manufacturing an arc welding joint according to any one of claims 1 to 5, characterized in that: The above-mentioned oscillation frequency f is less than 10 Hz.

7. The method for manufacturing an arc welding joint according to any one of claims 1 to 6, characterized in that: The above-mentioned arc welding is metal active gas shielded welding.

8. An arc welding joint comprising: The first steel plate part; a second steel plate portion overlapping the first steel plate portion in a plate thickness direction; and The weld bead joins the end of the first steel plate portion disposed on the surface of the second steel plate portion to the surface of the second steel plate portion. A zinc-based plating layer exists in a region of the surface of the second steel plate portion where the weld bead is not provided, The width w of the weld bead and the thickness tL of the second steel plate portion satisfy 3.3≤w / tL≤7.0, The porosity defect rate of the stable portion of the weld bead is less than 10%.

9. The arc welding joint according to claim 8, characterized in that: The Si content of the weld bead is 0.5 mass % or less.

10. The arc welding joint according to claim 8 or 9, characterized in that: In the stable portion of the weld bead, the weld toe on the second steel plate portion side has a wavy shape. The wavelength Y of the weld toe and the plate thickness tL of the second steel plate portion satisfy 0.7≤Y / tL≤2.

8.

11. The arc welding head according to any one of claims 8 to 10, characterized in that: The weld bead does not penetrate the second steel plate portion in the plate thickness direction.

12. The arc welding head according to any one of claims 8 to 11, characterized in that: In a cross section along the plate thickness direction, an outer edge of the weld bead intersects a butt surface between the first steel plate portion and the second steel plate portion.

13. An automobile component, wherein: An arc welding head according to any one of claims 8 to 12.

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