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

Abstract

A method for manufacturing an arc welded joint according to an embodiment of the present invention comprises: stacking a first steel sheet and a second steel sheet in a sheet thickness direction so that an end portion of the first steel sheet is disposed on the surface of the second steel sheet; and arc-welding the end portion of the first steel sheet and the surface of the second steel sheet, the end portion being laid over the surface, to form a weld bead. The surface of the second steel sheet has a zinc-based plating. The arc welding is weaving arc welding in which the torch performs a periodically undulating motion in a direction transverse to the welding direction. The sheet thickness tL (mm) of the second steel sheet and the weaving wavelength y (mm) of the torch during weaving arc welding have values such that y / tL≤2.8 is satisfied. The width w (mm) of the weld bead and the sheet thickness tL of the second steel sheet have values such that 3.3≤w / tL≤7.0 is satisfied. During the weaving arc welding, a droplet transfer frequency D (times / second) from the torch to a molten pool and the undulation frequency f (Hz) have values such that D / f≥25 is satisfied.

Description

Arc welded joint manufacturing method, arc welded joint, and automobile part

[0001] This application claims priority to Japanese Patent Application No. 2022-098078, filed on June 17, 2022, the contents of which are incorporated herein by reference.

[0002] Automotive parts such as suspension components are mainly made of hot-rolled steel sheets, which are often joined by arc welding.

[0003] In recent years, as the steel sheets used in automotive parts have become thinner and stronger, the level of corrosion resistance required for welded joints has also improved. As a result, there is a growing need to use zinc-based plated steel sheets, which have excellent corrosion resistance, as materials for automotive parts.

[0004] It is known that arc welding of zinc-based plated steel sheets is prone to the formation of voids called porosity defects in the weld bead. As shown in Figure 3, during normal arc welding, the zinc-based coating 14, which has a lower melting point and boiling point than iron, evaporates and becomes zinc vapor 14v. If the zinc vapor 14v remains in the molten pool 13P and the molten pool 13P solidifies, porosity defects pd will form in the weld bead 13. The molten pool 13P is a pool of molten metal created by the heat of the arc or other source during welding.

[0005] An example of an X-ray image of a conventional arc-welded joint in which porosity defects have occurred is shown in Figure 6. In the arc-welded joint shown in the image of Figure 6, a large number of porosity defects pd, shown in dark colors, are contained within weld bead 13, shown in light colors.

[0006] If a large number of porosity defects occur, the joining area of ​​the steel sheets decreases, which reduces the joint strength. Porosity defects also cause pits that reduce electrodeposition paintability. Pits are open pores that reach the surface of the weld bead. Pits cause unevenness on the surface of the weld bead, which can lead to electrodeposition paint defects. Even a small number of porosity defects can reduce electrodeposition paintability.

[0007] For the above reasons, there is a need for a technology that can suppress the occurrence of porosity defects in welded joints obtained by arc welding of zinc-based coated steel sheets.

[0008] Patent Document 1 discloses a TIG welding method for fillet joints using galvanized or primer-coated steel sheets, which uses a TIG arc oscillating at a frequency of 10 Hz or more and an amplitude of 3 mm or more, employing welding conditions including an arc current and welding speed that melt the surfaces of the base metals constituting the lap joint while not melting the joint corners, and feeding an additive wire toward the molten pool along the base metal corners from the welding direction to form a weld metal deposit while forming a gap between the wire and the base metal at the joint corners, and welding while allowing zinc vapor generated on the base metal surface near the bottom of the molten pool to escape from the gap to the outside. This welding method is said to achieve porosity- and pit-free welding by constantly maintaining a path for easy exhaust of zinc vapor or primer component vapor from the heat-affected zone adjacent to the molten pool in the closely-contacted lap joint of the galvanized or primer-coated steel sheets.

[0009] Japanese Patent Application Laid-Open No. 2003-53544

[0010] However, the technology disclosed in Patent Document 1 requires that the corners of the joint not be melted. Therefore, it is difficult to ensure the penetration depth of the weld bead using the technology disclosed in Patent Document 1. Furthermore, the technology disclosed in Patent Document 1 requires that the welding method be Tungsten Inert Gas (TIG) welding. Tungsten Inert Gas (TIG) welding is an arc welding method in which an arc is generated using non-consumable tungsten as an electrode and a filler material such as a welding wire is introduced 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 applicable to various arc welding methods, not limited to Tungsten Inert Gas (TIG) welding, is needed.

[0011] An object of the present disclosure is to provide a method for manufacturing an arc-welded joint that can suppress porosity defects in welding of zinc-based plated steel sheets, and an arc-welded joint and an automotive component that are made of zinc-based plated steel sheets and have suppressed porosity defects.

[0012] The gist of the present disclosure is as follows.

[0013] (1) A method for manufacturing an arc-welded joint according to one aspect of the present invention includes overlapping a first steel plate and a second steel plate in a plate thickness direction so that an end of the first steel plate is positioned on a surface of the second steel plate, and arc-welding the end of the overlapped 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-based plating, and the arc welding is performed by periodically oscillating a torch in a direction transverse to the welding direction. (2) Preferably, in the method for producing an arc-welded joint described in (1) above, the thickness tL (mm) of the second steel plate and the wavelength y (mm) of the torch waviness in the weaving arc welding are set to values ​​that satisfy 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 ​​that satisfy 3.3≦w / tL≦7.0, and the droplet transfer frequency D (times / second) from the torch to the molten pool and the oscillation frequency f (Hz) in the weaving arc welding are set to values ​​that satisfy D / f≧25. (3) Preferably, in the method for producing an arc-welded joint described in (1) above, the Si content of the weld bead is set to 0.5 mass% or less. (4) Preferably, in the method for producing an arc-welded joint described in (1) or (2) above, the wavelength y of the torch waviness and the thickness tL of the second steel plate are set to values ​​that satisfy 0.7≦y / tL. (4) Preferably, in the method for manufacturing an arc welded joint described in any one of (1) to (3) above, the weld bead does not penetrate the second steel plate in the plate thickness direction. (5) Preferably, in the method for manufacturing an arc welded joint described in any one of (1) to (4) above, the outer edge of the weld bead intersects with the mating surfaces of the first steel plate and the second steel plate in a cross section along the plate thickness direction. (6) Preferably, in the method for manufacturing an arc welded joint described in any one of (1) to (5) above, the oscillation frequency f is less than 10 Hz. (7) Preferably, in the method for manufacturing an arc welded joint described in any one of (1) to (6) above, the arc welding is Metal Active Gas welding.

[0014] (8) Another aspect of the present invention provides an arc-welded joint comprising a first steel plate portion, a second steel plate portion overlapping the first steel plate portion in the thickness direction, and a weld bead joining an end of the first steel plate portion arranged on the surface of the second steel plate portion to the surface of the second steel plate portion, wherein a zinc-based plating is applied to an area 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 the relationship 3.3≦w / tL≦7.0, and the porosity defect rate in the steady portion of the weld bead is less than 10%. (9) Preferably, in the arc-welded joint described in (8) above, the Si content of the weld bead is 0.5 mass% or less. (10) Preferably, in the arc-welded joint described in (8) or (9) above, the toe of the steady portion of the weld bead on the side of the second steel plate portion has a wavy shape, and the wavelength Y of the toe and the plate thickness tL of the second steel plate portion satisfy 0.7≦Y / tL≦2.8. (11) Preferably, in the arc-welded joint described in any of (8) to (10) above, the weld bead does not penetrate the second steel plate portion in the plate thickness direction. (12) Preferably, in the arc-welded joint described in any of (8) to (11) above, the outer edge of the weld bead intersects with the mating surfaces of the first steel plate portion and the second steel plate portion in a cross section along the plate thickness direction.

[0015] (13) An automobile component according to another aspect of the present invention includes the arc-welded joint according to any one of (8) to (12) above.

[0016] According to the present disclosure, it is possible to provide a method for manufacturing an arc-welded joint that can suppress porosity defects in welding of zinc-based plated steel sheets, and an arc-welded joint that is made of zinc-based plated steel sheets and has suppressed porosity defects.

[0017] FIG. 1 is a conceptual diagram of a manufacturing method of an arc welded joint according to the present embodiment, as seen in a plan view. FIG. 2 is a conceptual diagram of a manufacturing method of an arc welded joint according to the present embodiment, as seen in a cross section perpendicular to the welding direction. FIG. 3 is a cross-sectional view of an arc welded joint in which porosity defects have occurred in the weld bead. FIG. 4 is a plan view of an example of an arc welded joint according to the present embodiment. FIG. 5 is an X-ray image of an example of an arc welded joint according to the present embodiment. FIG. 6 is an X-ray image of an example of a conventional arc welded joint in which porosity defects are included. FIG. 7 is a plan view of an example of a weld bead in which the toe of the steady portion has a wavy shape. FIG. 8 is a cross-sectional view of an example of an arc welded joint in which a gap is present near the root R. FIG. 9 is a cross-sectional view of an example of an arc welded joint in which the outer edge of the weld bead intersects with the mating surfaces of the first steel plate portion and the second steel plate portion.

[0018] As shown in Figs. 1 and 2 , for example, a method for manufacturing an arc welded joint 1 according to one aspect of the present disclosure includes overlapping a first steel plate 11 and a second steel plate 12 in the plate thickness direction so that an end of the first steel plate 11 is disposed 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, wherein the surface 121 of the second steel plate 12 has a zinc-based plating 14, and the arc welding is performed by moving a torch A transversely to the welding direction WD. The weaving arc welding is performed by periodically oscillating the torch A in a direction perpendicular to the weaving arc welding direction, and the thickness tL (mm) of the second steel plate 12 and the wavelength y (mm) of the undulations of the torch A in the weaving arc welding are set to values ​​that satisfy 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 ​​that satisfy 3.3≦w / tL≦7.0, and the droplet transfer frequency D (times / second) from the torch A to the molten pool 13P and the oscillation frequency f (Hz) in the weaving arc welding are set to values ​​that satisfy D / f≧25. Alternatively, a method for manufacturing an arc-welded joint according to one aspect of the present disclosure includes a step of arc-welding an end surface of a first steel sheet and a surface of a second steel sheet to form a weld bead, wherein the surface of the second steel sheet to be arc-welded has a zinc-based coating, the arc welding is weaving arc welding, the sheet thickness tL (mm) of the second steel sheet and the wavelength y (mm) of the waviness of a torch A in the weaving arc welding satisfy y / tL≦2.8, the width w (mm) of the weld bead and the sheet thickness tL of the second steel sheet satisfy 3.3≦w / tL≦7.0, and the droplet transfer frequency D (times / second) from the torch to the molten pool and the oscillation frequency f (Hz) in the weaving arc welding satisfy D / f≧25. This manufacturing method is described in detail below. Note that the definitions of terms used in the manufacturing method of an arc-welded joint below also apply to terms used in the arc-welded joint.

[0019] The present inventors have conducted extensive research into methods for reducing porosity defects (pd) in weld beads 13 obtained by arc welding of zinc-based coated steel sheets, and have found that the amount of porosity defects (pd) can be dramatically reduced by (1) performing weaving arc welding under specified conditions, in which torch A is periodically oscillated in a direction transverse to the welding direction (WD), and (2) controlling the frequency (D) of droplet transfer from torch A to molten pool 13P during arc welding within a specified range.

[0020] The weaving method is a welding technique in which a weld bead 13 is formed by periodically oscillating an arc welding torch A in a direction transverse to a welding direction WD. The welding direction WD refers to the extension direction of the weld bead 13 obtained by welding. Weaving arc welding is arc welding performed according to the weaving method. An example of a typical weaving arc welding trajectory is a sine wave. In this case, the torch travels at a constant speed along the welding direction WD, and the torch moves in a simple harmonic motion along a direction perpendicular to the WD. However, various trajectories can be formed by periodically varying the torch speed along the welding direction WD and the speed along a direction perpendicular to the WD.

[0021] Generally, weaving beads obtained by the weaving method, in which the torch A is periodically oscillated in a direction transverse to the welding direction WD, tend to be wider than conventional weld beads. For example, the ratio of penetration width to penetration depth in weaving beads is often larger than in conventional weld beads. Therefore, when weaving arc welding zinc-based coated steel sheets, the amount of zinc-based coating 14 introduced into the molten pool 13P is greater than in conventional arc welding. For this reason, weaving arc welding has traditionally been considered undesirable from the perspective of suppressing porosity defects (pd) caused by the zinc-based coating 14. In the welding method disclosed in Patent Document 1, a Tungsten Inert Gas (TIG) arc is oscillated, but at the same time, gaps are provided at the corners to allow zinc vapor to escape from the molten metal.

[0022] However, the inventors have discovered that the amount of porosity defects pd can be dramatically reduced by (1) performing weaving arc welding under specified conditions and (2) increasing the droplet transfer frequency D from the torch A to the molten pool 13P. The droplet transfer frequency D refers to the frequency of occurrence of the phenomenon in which droplets d transfer from the tip of the welding wire AW to the molten pool 13P across the arc generation zone. The droplets d are molten metal droplets formed when the welding wire AW is melted by the heat of the arc or the like. It is presumed that the frequent falling of droplets d into the molten metal stirs the molten metal in the molten pool 13P, further accelerating the emission of zinc vapor 14v from the molten pool 13P.

[0023] Furthermore, weaving is necessary to stir the molten pool 13P, but the inventors have found that an excessively high oscillation frequency during weaving arc welding is undesirable. Therefore, (3) the droplet transfer frequency D and the oscillation frequency f during weaving arc welding must satisfy D / f ≥ 25. The oscillation frequency f of the torch A is the reciprocal of the length (in seconds) of one period when the torch A is oscillated periodically.

[0024] The reason for specifying D / f is as follows: In order to promote the discharge of zinc vapor from the molten pool, it is necessary to actively stir the molten pool. In this case, it is necessary to combine the stirring of the molten metal using droplets d with weaving arc welding. Although an increase in the droplet transfer frequency D is thought to help promote the above-mentioned discharge of zinc, according to the inventors' investigations, the porosity defect rate when weaving is not performed does not decrease sufficiently even when the droplet transfer frequency D is increased.

[0025] On the other hand, when welding was performed with D / f ≥ 25, the porosity defect rate decreased. This is thought to be because weaving welding allowed droplets d to be transferred to various locations in the molten pool 13P, further increasing the agitation of the molten pool 13P. In other words, as shown in Figure 1, the trajectory of torch A is not linear. Instead, weaving welding creates a non-linear trajectory, such as a sine wave, which is thought to be necessary to transfer droplets d evenly throughout the molten pool 13P. In other words, droplets d are transferred not only in the welding direction but also in a direction transverse to the welding direction. This promotes agitation of the molten pool 13P not only in the welding direction but also in the width direction, effectively reducing the porosity defect rate.

[0026] However, when the oscillation frequency f was large relative to the droplet transfer frequency D and D / f ≥ 25 was not satisfied, the porosity defect rate was not sufficiently reduced. This suggests that if the droplets d do not transfer continuously for a certain period of time, tracing the weaving trajectory of the torch A during weaving welding, that is, if the droplets d do not transfer without too much spacing, the molten pool 13P will not be stirred sufficiently. The above formula means that the number of droplets d transferred per oscillation cycle of the torch A is 25 or more. Furthermore, if the oscillation frequency f is too high, arc welding may become unstable. For these reasons, satisfying D / f ≥ 25 is also necessary to reduce the porosity defect rate of the arc-welded joint 1.

[0027] A method for manufacturing the arc welded joint 1 according to this embodiment, which is obtained based on the above technical concept, will be described in detail below.

[0028] In the manufacturing method for the arc welded joint 1 according to this 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 positioned 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 arc welding, the first steel plate 11 and the second steel plate 12 are overlapped. Furthermore, the weld bead 13 is formed 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 according to this embodiment is a so-called lap fillet joint.

[0029] 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, the flange portion of a hat-shaped member is also considered to be a steel plate according to this embodiment.

[0030] Of the first steel sheet 11 and the second steel sheet 12, at least the surface 121 of the second steel sheet 12 where the first steel sheet 11 is overlapped (i.e., the surface 121 to be arc-welded) has a zinc-based coating 14. This improves the corrosion resistance of the arc-welded joint 1. More preferably, both surfaces of the second steel sheet 12 have the zinc-based coating 14. Even more preferably, one or both surfaces of the first steel sheet 11 also have the zinc-based coating 14. The zinc-based coating 14 refers to a coating having a composition mainly composed of zinc and, in some cases, further containing elements such as Si, Al, Mg, and Fe. "The zinc-based coating has a composition mainly composed of zinc" means that the element contained in the zinc-based coating in the largest amount 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 mass% or more.

[0031] Plating processes include electroplating and hot-dip galvanizing, and in some cases, the steel sheet and the coating are alloyed by heat treatment after coating. All of the examples of zinc-based coatings 14 described above have a sacrificial corrosion protection effect. The components of the zinc-based coating 14 are measured by the following method. First, an acid containing an inhibitor that suppresses corrosion of the steel is used to peel off and dissolve the coating layer to obtain an acid solution. Next, the obtained acid solution is subjected to ICP analysis. This allows the components of the zinc-based coating 14 to be identified. There are no particular restrictions on the type of acid, as long as it is an acid that can dissolve the zinc-based coating 14. Note that the components measured by the above-mentioned means are the average components of the entire coating layer.

[0032] Because the zinc-based coating 14 is applied to the arc-welded surface 121 of the second steel sheet 12, a large amount of zinc is mixed into the molten pool 13P formed by arc welding. Because zinc has a lower melting point and boiling point than iron, the zinc in the molten pool 13P evaporates during arc welding, becoming zinc vapor 14v. If the zinc vapor 14v remains in the molten pool 13P and the molten pool 13P solidifies, porosity defects pd occur in the weld bead 13. The molten pool 13P is a pool of molten metal created by the heat of the arc or the like during welding. To solve this problem, the weaving conditions and droplet transfer frequency D are specified for the arc-welded joint 1 according to this embodiment as described below.

[0033] (1. Weaving Conditions) The arc welding is weaving arc welding. In weaving arc welding, the torch A is periodically oscillated in a direction transverse to the welding direction WD. The weaving arc welding is performed so as to satisfy the following formulas 1 and 2. 3.3≦w / tL≦7.0 (Equation 2) Here, the symbols included in the above equation are defined as follows: y: wavelength (mm) of the undulation of torch A in weaving arc welding (i.e., the trajectory formed by the periodic oscillation of torch A) In other words, y is the distance traveled by the periodically oscillating torch A along the welding direction WD per period tL: thickness (mm) of the second steel plate 12 v: moving speed (m / min) of torch A along the welding direction WD f: oscillation frequency (Hz) of torch A w: width (mm) of the weld bead 13 Note that the coefficient "50 / 3" (i.e., "1000 / 60") included in equation 1 is determined by the unit of the torch moving speed v, "m / min," and the unit of the oscillation frequency f, "Hz" (i.e., "sec"). －１ ") and the unit "mm" of the wavelength y of the swell.

[0034] The values ​​corresponding to these codes are explained in more detail below.

[0035] As described above, in weaving arc welding, the weld bead 13 is formed while periodically oscillating the arc welding torch A in a direction transverse to the welding direction WD. In weaving arc welding in which the torch A is oscillated periodically, the wavelength y of the waviness of the torch A refers to the distance traveled by the torch A along the welding direction WD during one cycle of the weaving arc welding. FIG. 1 shows an example of the waviness wavelength y. The waviness wavelength y refers to the travel distance measured along the welding direction WD. The travel distance of the torch along the torch trajectory (the dashed line shown in FIG. 1) and the wavelength y of the torch waviness are different concepts.

[0036] The moving speed v of the torch A along the welding direction WD is a value obtained by dividing the moving distance of the torch A along the welding direction WD by the time required for the movement. The moving speed in the direction transverse to the welding direction WD is not included in v.

[0037] The oscillation frequency f of the torch A is the reciprocal of the length (seconds) of one period when the torch A is oscillated periodically.

[0038] The width w of weld bead 13 refers to the length (width) of weld bead 13 measured along the welding direction WD, i.e., the direction perpendicular to the extension direction of weld bead 13 .

[0039] 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. If 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. The plate thickness is measured at at least two locations within a range of 10 mm from the toe of the weld bead in a direction perpendicular to the extending direction of the weld bead and is regarded as the plate thickness tL of the second steel plate 12. The plate thickness may be measured using a micrometer or vernier calipers, or may be measured by cutting and observing a cross section taken under a microscope.

[0040] As shown in Equation 1, the wavelength y of the waviness of torch A is a function of the movement speed v of torch A and the oscillation frequency f of torch A. The inventors determined the upper limit of the wavelength y of the waviness of torch A according to the thickness tL of the second steel plate 12. The greater the thickness of the second steel plate 12 (corresponding to the so-called "bottom plate" in a lap fillet weld joint), the greater the heat input required in arc welding. In general arc welding, the heat input is set to a level that ensures a penetration depth of about half the thickness of the bottom plate. The greater the thickness tL of the bottom plate, the greater the required heat input, and the greater the amount of zinc vapor 14v generated. Therefore, the thickness tL of the bottom plate is also taken into consideration when determining the wavelength y of the waviness to suppress zinc vapor 14v.

[0041] If y / tL exceeds 2.8, the molten pool 13P may solidify before the zinc vapor 14v is discharged from the molten pool 13P, increasing the risk of porosity defects pd occurring 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.

[0042] 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 porosity defects pd in the weld bead 13, the smaller y is, the better. However, as y becomes smaller, the movement speed v of the torch A becomes slower, resulting in reduced welding efficiency. Furthermore, as y becomes smaller, the oscillation frequency f of the torch A becomes higher, which may result in unstable arc welding. In addition, by increasing the wavelength y of the waviness of the torch A, waviness is formed in the weld bead 13, resulting in an improved fatigue strength, as described below. From the viewpoint of ensuring welding efficiency and welding stability, y / tL may be set to 0.7 or more.

[0043] Note that the wavelength y of the waviness of torch A during weaving arc welding often matches the wavelength of the waviness formed at toe 1311 of steady portion 131 of weld bead 13. However, there are cases where it is difficult to identify the wavelength of the waviness at toe 1311 of steady portion 131 of weld bead 13. In such cases, it is difficult to identify the wavelength y of the waviness of torch A based on an analysis of weld bead 13. In particular, when the wavelength y of the waviness of torch A is short and toe 1311 of steady portion 131 of weld bead 13 is not wavy, no direct trace of the waviness of torch A remains in weld bead 13.

[0044] Furthermore, as shown in Equation 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. If w / tL is too small, the molten pool 13P is not sufficiently stirred. On the other hand, if w / tL is too large, the molten pool 13P solidifies before it is stirred. In either case, zinc vapor 14v cannot be sufficiently discharged from the molten pool 13P. Therefore, w / tL is set to 3.3 or more and 7.0 or less. w / tL may also be set to 3.5 or more, 4.0 or more, or 4.5 or more. w / tL may also be set to 6.5 or less, 6.0 or less, or 5.5 or less.

[0045] There is a good correlation between the width w (mm) of the weld bead 13 and the oscillation amplitude x (mm) of the torch A. As shown in FIG. 1 , in weaving arc welding, in which the arc welding torch A is periodically moved transversely to the welding direction WD, the oscillation amplitude x of the torch A is half the width of the range of movement of the torch A during one period. The "width" refers to the width measured along a direction perpendicular to the welding direction WD. Furthermore, the width w of the weld bead 13 is affected not only by the oscillation amplitude x of the torch A, but also by the current value, voltage value, welding speed (i.e., the movement speed v of the torch A along the welding direction WD), and the components of the molten pool 13P. By appropriately controlling these factors, it is possible to produce a weld bead 13 having a width close to the target value.

[0046] (2. Droplet Transfer Frequency) In arc welding, the droplet transfer frequency D (times / second) from the torch A to the molten pool 13P and the oscillation frequency f must be set to values ​​that satisfy D / f≧25. The droplets d that drip into the molten pool 13P agitate the molten pool 13P, further promoting the discharge of zinc vapor 14v from the molten pool 13P. However, if D / f is less than 25, this effect cannot be fully achieved. Therefore, D / f is set to 25 or more. D / f may also be set to 27 or more, 30 or more, or 35 or more. The upper limit of D / f is not particularly limited, but may be, for example, 55 or less, 50 or less, or 48 or less.

[0047] The droplet transfer frequency D can be controlled by performing pulse arc welding. Pulse arc welding is an arc welding method in which the current is periodically increased and decreased to create a pulsed current waveform. There is a correlation between the pulse frequency and the droplet transfer frequency D, and generally, the droplet transfer frequency D increases as the pulse frequency increases. The droplet transfer frequency D is also slightly affected by the feed rate 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, it is possible to identify the welding conditions for obtaining the desired droplet transfer frequency D.

[0048] The droplet transfer frequency D can be measured by observing the molten pool 13P using a high-speed camera. However, after the molten pool 13P solidifies, no direct traces of the droplet transfer frequency D remain on the weld bead 13. Therefore, the droplet transfer frequency D must be measured during arc welding. However, it is not necessary to measure the droplet transfer frequency D constantly during arc welding. If the above-mentioned welding conditions that affect the droplet transfer frequency D are constant, the droplet transfer frequency D will also be substantially constant. Therefore, in weaving arc welding that is performed under conditions that have been confirmed in advance to achieve a predetermined droplet transfer frequency D, the droplet transfer frequency D is considered to be at that predetermined value.

[0049] (Si Content of Weld Bead 13) In the manufacturing method of the arc-welded joint 1 according to this embodiment, the Si content of the weld bead 13 is preferably 0.5 mass% or less. The inventors have discovered that reducing the Si content of the molten pool 13P further reduces porosity defects (pd) in the weld bead 13 formed by solidification of the molten pool 13P. While the reason for this is unclear at present, it is presumed that a reduction in the Si content of the molten pool 13P reduces the viscosity of the molten pool 13P, further accelerating the discharge of zinc vapor 14v from the molten pool 13P. This effect is most pronounced 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 0.4 mass% or less, 0.3 mass% or less, or 0.2 mass% or less.

[0050] 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 chips using a known analytical method such as ICP. The Si content of the weld bead 13 is affected by the Si content of the first steel sheet 11 and the second steel sheet 12, the Si content of the wire, and the mixing ratio of the base metal components and the wire components. Therefore, the Si content of the weld bead 13 can be controlled by selecting the wire components and the mixing ratio of the base metal components and the wire components that are suitable for the components of the steel sheets to be welded.

[0051] (Preferable Lower Limit of Wavelength y of Torch Waviness) When the wavelength y of the waviness of torch A during weaving arc welding is large, the toe 1311 of the steady portion 131 of the weld bead 13 has a wavy shape that reflects the weaving of torch A. The toe 1311 is the line where the surface of the base metal intersects with the surface of the weld bead 13. On the other hand, when the wavelength y of the waviness of torch A is small, no wavy shape is observed at the toe 1311. In normal weaving arc welding, from the viewpoint of shaping the weld bead 13 and improving its appearance, the wavelength y is often reduced to prevent the toe 1311 from having a wavy shape. However, the present inventors have discovered that the fatigue strength of the arc welded joint 1 is improved by making the shape of the toe 1311 on the second steel plate 12 side wavy. The inventors presume that this is because the stress applied to the weld bead 13 is preferably dispersed by making the shape of the toe 1311 wavy.

[0052] (Prevention of strike-through) The higher the heat input in arc welding, the deeper the weld pool 13P becomes. As a result, the weld pool 13P may penetrate the second steel sheet 12, exposing the weld bead 13 on the back side of the second steel sheet 12. This phenomenon is generally referred to as "strike-through." When strike-through occurs, the molten metal that makes up the weld pool 13P drips, impairing welding workability. Furthermore, if the second steel sheet 12 has a zinc-based coating 14 on both surfaces, strike-through causes the zinc-based coating 14 on the back side of the second steel sheet 12 to mix with the weld pool 13P. This increases the amount of zinc vapor 14v and increases porosity defects pd.

[0053] Therefore, in the manufacturing method of the arc-welded joint 1 according to this embodiment, it is preferable that the weld bead 13 does not penetrate the second steel plate 12 in the plate thickness direction. That is, in the manufacturing method of the arc-welded joint 1 according to this embodiment, it is preferable that the surface of the second steel plate 12 opposite to the surface 121 to be arc-welded is not melted during arc welding. In other words, it is preferable that the back surface of the second steel plate 12 remains solid during arc welding. This can further reduce the amount of porosity defects (pd). By reducing the heat input during arc welding and reducing the penetration depth of the weld bead 13, strike-through can be prevented.

[0054] (Ensuring Penetration Depth) On the other hand, from the viewpoint of stably ensuring the joining 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 according to this embodiment, it is preferable that the outer edge of the weld bead 13 intersects with the mating surfaces of the first steel plate and the second steel plate in a cross section along the plate thickness direction. That is, in the method for manufacturing the arc welded joint 1 according to this embodiment, as shown in Fig. 2 , the root R may be melted during arc welding, and the weld bead may grow to the mating surfaces of the first steel plate and the second steel plate.

[0055] The root R refers to the bottom portion where welding is performed, and more specifically, refers to the location where the end face 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 fusion boundary (the boundary between the weld bead 13 and the base material). The fusion boundary can be easily visualized by etching the cross section of the arc-welded joint 1.

[0056] If the penetration depth is shallow and the molten pool 13P does not reach the root R, a gap C will be formed near the root R, i.e., at the corner of the joint, as shown in Figure 8A. On the other hand, by forming the molten pool 13P to reach the root R, the penetration depth of the weld bead 13 is increased, making the corner of the joint solid as shown in Figure 8B, and ensuring stable joining strength of the arc-welded joint 1.

[0057] (Oscillation frequency f) In the manufacturing method of the arc welded joint 1 according to this embodiment, the oscillation frequency f of the weaving arc welding is preferably less than 10 Hz. By setting the oscillation frequency f to less than 10 Hz, the stability of the arc welding can be further improved. The oscillation frequency f may be set to 9 Hz or less, 8 Hz or less, or 7 Hz or less.

[0058] (Types of Arc Welding) Metal Active Gas (MAG) welding is preferred for arc welding. Among arc welding methods, Tungsten Inert Gas (TIG) welding and plasma arc welding described in Patent Document 1 are non-consumable electrode welding methods, and therefore cannot achieve molten pool agitation that combines weaving and droplet transfer. Unlike Metal Active Gas (MAG) welding, Metal Active Gas (MIG) welding uses an inert gas, primarily argon or helium, as a shielding gas, but this gas is expensive. In addition, the tendency of the arc to spread can sometimes prevent sufficient penetration. On the other hand, Metal Active Gas (MAG) welding does not have these drawbacks.

[0059] Next, an arc welded joint 1 according to another aspect of the present disclosure will be described. The arc welded joint 1 according to this 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 that joins an end of the first steel plate portion 21 arranged on a surface 121 of the second steel plate portion 22 to the surface 121 of the second steel plate portion 22, a zinc-based plating 14 is formed in an area of ​​the surface 121 of the second steel plate portion 22 where the weld bead 13 is not provided, 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 in a steady portion 131 of the weld bead 13 is less than 10%. The arc welded joint according to this embodiment comprises a first steel plate, a second steel plate overlapping the first steel plate, and a weld bead extending linearly along an edge of the first steel plate and joining the edge of the first steel plate to a surface of the second steel plate, the second steel plate having a zinc-based plating on the surface on which the weld bead is provided, the width w of the weld bead and the thickness tL of the second steel plate satisfy the relationship 3.3≦w / tL≦7.0, and the porosity defect rate in the steady portion of the weld bead is less than 10%.

[0060] The arc welded joint 1 according to this embodiment has a first steel plate portion 21 and a second steel plate portion 22 superimposed on 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 this embodiment, the steel plate as a component of the welded joint is referred to as a "steel plate portion," and the steel plate as a raw material of the welded joint is referred to as a "steel plate."

[0061] As with the above-described "steel plate," the concept of "steel member" includes not only plate-shaped members but also plate-shaped portions of members having a three-dimensional shape. For example, the flange portion of a hat-shaped member is also considered to be a steel member according to this embodiment. Other preferred aspects of the above-described 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.

[0062] Furthermore, the arc welded joint 1 according to this embodiment has a weld bead 13 that joins the end of the first steel plate portion 21, which is 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 welded joint 1 according to this embodiment is a so-called lap fillet joint.

[0063] The surface 121 of the second steel plate portion 22 is provided with a zinc-based plating 14. That is, of the first steel plate portion 21 and the second steel plate portion 22, at least the surface 121 on which the weld bead 13 is disposed has the zinc-based plating 14 on part or all of it. This improves the corrosion resistance of the arc-welded joint 1. However, the zinc-based plating 14 is not present in the region where the weld bead 13 is provided. That is, the zinc-based plating 14 is present in the region of the surface of the second steel plate portion 22 on which the weld bead 13 is not provided. More preferably, both surfaces of the second steel plate portion 22 have the zinc-based plating 14. Even more preferably, one or both surfaces of the first steel plate portion 21 also have the zinc-based plating 14.

[0064] (Width w of Weld Bead and Porosity Defect Rate) In the arc welded joint 1 according to this 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 in the steady portion 131 of the weld bead 13 is less than 10%. Such a weld bead 13 can be produced, for example, by arc welding, as in the method for producing the arc welded joint 1 according to this embodiment described above, which includes: (1) performing weaving arc welding under predetermined conditions; and (2) setting the droplet transfer frequency D from the arc welding torch A to the molten pool 13P within a predetermined range. By keeping the porosity defect rate less than 10%, the joint strength of the arc welded joint 1 can be improved and electrodeposition coating defects can be suppressed.

[0065] The steady portion 131 of the weld bead 13 is the region of the weld bead 13 other than the starting portion 132 and the terminal portion 133. As illustrated in the image of Figure 5, the starting portion 132 and the terminal portion 133 of the weld bead 13 are formed when the welding arc is not stable, and therefore have non-uniform widths and shapes. In the arc welded joint 1 according to this embodiment, the region within 15 mm from the starting end of the weld bead 13 is defined as the starting portion 132, the region within 15 mm from the terminal end is defined as the terminal portion 133, and the remaining regions are defined as the steady portion 131.

[0066] The porosity defect rate in the steady portion 131 of the weld bead 13 is measured by the following procedure. First, an X-ray transmission image of the steady portion 131 of the weld bead 13 is taken. This makes it possible to confirm the porosity defects pd contained in the weld bead 13. Next, the total length of the porosity defects pd along the weld bead 13 is measured. Then, the total length of the porosity defects pd is divided by the length of the steady portion 131 to calculate the porosity defect rate.

[0067] To illustrate a method for measuring the porosity defect rate, FIG. 5 shows an X-ray transmission image of a weld bead 13 in which the porosity defect rate in the steady portion 131 is 0%, and FIG. 6 shows an X-ray transmission image of a weld bead 13 in which the porosity defect rate in the steady portion 131 is 52.0%. Since no porosity defects pd are observed in the image of FIG. 5, the total length of the porosity defects pd along the weld bead 13 is considered to be 0 mm. In the image of FIG. 6, many porosity defects pd are observed in the weld bead 13. These porosity defects pd are projected onto a line along the weld bead 13, and are shown above the weld bead 13 in FIG. 6. The sum of the projection lines is the total length of the porosity defects pd along the weld bead 13.

[0068] (Si Content of Weld Bead 13) In the arc welded joint 1 according to this embodiment, it is further preferable that the Si content of the weld bead 13 is 0.5 mass% or less. This further reduces porosity defects pd. The Si content of the weld bead 13 may also be 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 method described above.

[0069] (Shape of toe 1311 on the second steel plate portion 22 side of steady portion 131 of weld bead 13) As shown in Fig. 7 , toe 1311 on the second steel plate portion 22 side of steady portion 131 of weld bead 13 may have a wavy shape. Here, the wavy shape refers to a shape in which concave portions and convex portions appear alternately and periodically. The wavelength Y of toe 1311 and the plate thickness tL of second steel plate portion 22 may satisfy 0.7 ≤ Y / tL ≤ 2.8.

[0070] In ordinary weaving arc welding, from the viewpoint of shaping the weld bead 13 and improving its appearance, it is often the case that the wavelength y of the torch waviness is reduced so as not to provide a wavy shape to the toe 1311. In the arc welded joint 1 according to this embodiment, from the viewpoint of suppressing porosity defects, it is not necessary to provide a wavy shape to the toe 1311. However, the present inventors have found that by providing a wavy shape to the toe 1311 on the side of the second steel plate portion 22, the fatigue strength of the arc welded joint 1 is improved. The present inventors believe that this is because the wavy shape of the toe 1311 allows the stress applied to the weld bead 13 to be preferably distributed.

[0071] However, as the wavelength Y of the weld toe becomes smaller, the wavy shape of the weld toe becomes less visible, and the effect of improving fatigue strength also becomes less likely to be obtained. From the viewpoint of ensuring the effect of improving fatigue strength, it is preferable to set Y / t at 0.7≦Y / t. On the other hand, by setting Y / tL at 2.8, the occurrence of porosity defects pd in the weld bead 13 can be effectively suppressed. Therefore, the wavelength Y of the weld toe 1311 on the second steel plate portion 22 side of the steady portion 131 of the weld bead 13 and the plate thickness tL of the second steel plate portion 22 may satisfy Y / tL≦2.8.

[0072] However, as described above, from the viewpoint of reducing porosity defects, the wavelength y in weaving arc welding may be reduced to make the weld toe 1311 smooth enough that no wavy shape is visible. Even if no wavy shape is visible at the weld toe 1311 of the weld bead 13, if the ratio of the width of the weld bead 13 in the steady portion to the penetration depth of the weld bead 13 measured in a cross section perpendicular to the extension direction of the weld bead 13 (weld bead width ÷ penetration depth) exceeds 10, the weld bead 13 is presumed to have been formed by weaving arc welding. The penetration depth is the maximum depth of the weld bead 13 measured in the cross section, with the surface 121 of the second steel plate portion 22 as the reference.

[0073] (Prevention of Strike-Through) High heat input during arc welding can cause Strike-Through. When Strike-Through occurs, the molten metal forming the weld pool 13P drips, impairing welding workability. Furthermore, if the second steel plate portion 22 has zinc-based plating 14 on both surfaces, Strike-Through can cause the zinc-based plating 14 on the back side of the second steel plate portion 22 to mix with the weld pool 13P. This increases the amount of zinc vapor 14v and the number of porosity defects (pd). Therefore, in the arc-welded joint 1 according to this embodiment, it is preferable that the weld bead 13 does not penetrate the second steel plate portion 22 in the thickness direction. That is, in the arc-welded joint 1 according to this embodiment, it is preferable that the weld bead 13 is not exposed on the surface of the second steel plate portion 22 opposite the surface 121 on which the weld bead 13 is provided. This can further reduce the number of porosity defects (pd).

[0074] (Ensuring Penetration Depth) 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, as shown in FIG. 8B , in the arc welded joint 1 according to the present embodiment, in a cross section taken along the plate thickness direction, the weld bead 13 may include a root R, which is a point where the end face of the first steel plate portion 21 and the surface of the second steel plate portion 22 intersect. In other words, in a cross section of the arc welded joint 1 taken along the extension direction of the weld bead 13, the outer edge of the weld bead 13 may intersect with the mating surfaces of the first steel plate portion 21 and the second steel plate portion 22. By growing the weld bead 13 beyond the root R so that the mating surfaces of the first steel plate portion 21 and the second steel plate portion 22 intersect with the outer edge of the weld bead 13, the penetration depth of the weld bead 13 can be increased, and the joint strength of the arc welded joint 1 can be stably ensured.

[0075] (Other Preferred Aspects) Various aspects other than those described above can be appropriately adopted for the method for manufacturing an arc welded joint 1 according to this embodiment, and for the arc welded joint 1. Examples of more preferred aspects are given below. Unless otherwise specified, the aspects exemplified below are applicable to both the method for manufacturing an arc welded joint 1 according to this embodiment, and the arc welded joint 1. Preferred aspects of the first steel plate 11 and the second steel plate 12, which are the raw materials for the arc welded joint, are also applicable to the first steel plate portion 21 and the second steel plate portion 22, which are components of the arc welded joint, respectively.

[0076] There are no particular limitations on the thickness of the first steel plate 11. For example, when the first steel plate 11 is used as 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, there are no particular limitations on the thickness tL of the second steel plate 12, and when this is used as a steel plate for automobiles, the thickness is preferably 0.8 mm or more and 4.0 mm or less.

[0077] The tensile strength of the first steel plate 11 is not particularly limited. For example, the tensile strength of the first steel plate 11 may be 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 may be 440 MPa or more and 1500 MPa or less. The chemical composition and metal structure of these steel plates are not particularly limited either, and known preferred configurations can be appropriately adopted.

[0078] The thickness and composition of the zinc-based plating 14 are not particularly limited. ２ More than 200g / m ２ Here, the coating weight of the zinc-based coating 14 means the total amount of zinc and other elements contained in the zinc-based coating 14. Examples of elements other than zinc contained in the zinc-based coating 14 include Si, Al, Mg, and Fe.

[0079] Only the coating amount of zinc contained in the zinc-based plating 14 may be separately specified. For example, if the zinc content per side of the zinc-based plating 14 is 20 g / m ２ The zinc content per side of the zinc-based coating 14 does not include the amounts of alloying elements other than zinc, such as Si, Al, Mg, and Fe. The coating weight per side refers to the coating weight of only the zinc-based coating 14 disposed on the surface of the second steel sheet 12 facing the first steel sheet 11, out of the two surfaces of the second steel sheet 12.

[0080] In the arc welded joint 1 according to this embodiment, the zinc-based plating 14 may be present within 100 μm of the weld bead 13. That is, the distance between the zinc-based plating 14 and the weld bead 13 is preferably 100 μm or less. This further improves corrosion resistance in the vicinity of the weld bead 13. The smaller the distance between the zinc-based plating 14 and the weld bead 13, the better, and it may even be 0 μm. That is, the zinc-based plating 14 and the weld bead 13 may be in contact with each other.

[0081] In the manufacturing method of the arc-welded joint 1 according to this embodiment, there is no need to remove the zinc-based coating from the surface 121 of the second steel sheet 12 before arc welding. During arc welding, the zinc-based coating 14 evaporates in the vicinity of the weld bead 13, which may cause a gap between the weld bead 13 and the zinc-based coating 14. However, by performing arc welding without removing the zinc-based coating 14 from the surface 121 of the second steel sheet 12, the gap between the zinc-based coating 14 and the weld bead 13 can easily be made 100 μm or less. If the zinc-based coating 14 were removed from the surface 121 of the second steel sheet 12 before arc welding, the gap between the weld bead 13 and the zinc-based coating 14 would exceed 100 μm in part or all of the toe of the weld bead 13.

[0082] Furthermore, it is sufficient that the zinc-based plating 14 is disposed at least on the surface 121 to be arc-welded of the second steel sheet 12. Therefore, a plating different from the zinc-based plating 14 may be provided on the surface of the first steel sheet 11 and the surface of the second steel sheet 12 on the side that is not arc-welded. An example of a plating different from the zinc-based plating 14 is aluminum plating.

[0083] Furthermore, for the purpose of improving corrosion resistance, etc., the arc welded joint 1 may have a coating film. The coating film is, for example, an electrodeposition coating film. The manufacturing method of the arc welded joint 1 may include, for example, a coating step such as an electrodeposition coating step.

[0084] The above-described configuration of the manufacturing method of the arc welded joint 1 according to this embodiment may be applied to at least a portion of the portion to be welded of the arc welded joint 1. The above-described configuration of the arc welded joint 1 may also be applied to at least a portion of the weld of the arc welded joint 1. Preferably, the above-described configuration is applied to the entire weld of the first steel plate 11 and the second steel plate 12. However, for example, in order to improve welding efficiency, the above-described configuration may be applied only to portions where suppression of porosity defects pd is strongly required, and the configuration of a normal arc welded joint 1 may be applied to other portions.

[0085] The shape of the trajectory of the torch A during weaving arc welding is not particularly limited as long as the above-mentioned requirements are satisfied. The trajectory of the torch A can be, for example, a sine wave shape. For example, the trajectory of the torch A can be made to have a sine wave shape by keeping the moving speed v of the torch A along the welding direction WD constant and oscillating the torch A in a direction perpendicular to the welding direction WD. On the other hand, the shape of the trajectory of the torch A can be varied in various ways by periodically varying the moving speed v of the torch A along the welding direction WD.

[0086] The application of the arc welded joint 1 according to this embodiment is not limited. For example, building materials and automobile parts are examples of suitable applications of the arc welded joint 1 according to this embodiment.

[0087] An automotive part according to another aspect of the present disclosure includes the arc-welded joint 1 according to the present embodiment described above. Therefore, the automotive part according to the present embodiment is made of a zinc-based plated steel sheet and therefore has excellent corrosion resistance. Furthermore, the automotive part according to the present embodiment has excellent joint strength and electrodeposition paintability because porosity defects are suppressed.

[0088] The effects of one embodiment of the present disclosure will be explained in more detail using examples. However, the conditions in the examples are merely examples of conditions adopted to confirm the feasibility and effects of the present disclosure. The present disclosure is not limited to this example of conditions. Various conditions may be adopted in the present disclosure as long as they do not deviate from the gist of the present disclosure and the object of the present disclosure is achieved.

[0089] Arc-welded joints were produced under various welding conditions by arc-welding the edge of a first steel plate and the surface of a second steel plate that were overlapped together to form a weld bead.

[0090] The thickness tL of the second steel plate, the width w of the weld bead, the wavelength y of the torch waviness, the torch oscillation amplitude x, the torch movement speed v along the welding direction, and the torch oscillation frequency f are shown in Table 1A or Table 1B. Additionally, Table 1B also shows D / f, the value obtained by dividing the droplet transfer frequency D by the torch oscillation frequency f. In some examples, the weld bead was produced by conventional arc welding rather than weaving arc welding. In examples where weaving arc welding was not performed, D / f is shown as "-". Furthermore, in the weaving arc welding device used by the inventors, there was a slight discrepancy between the set value and the actual value of the torch oscillation amplitude x. Table 1A lists both the set value and the actual value of the oscillation amplitude x for the device.

[0091] Table 2 shows the wavelength Y of the toe of the steady portion of the weld bead on the side of the second steel plate, and the Si content of the weld bead obtained by arc welding. For reference, the calculated values ​​of y / tL and w / tL are also shown in Table 2. Table 2 also shows the value obtained by dividing the width of the weld bead by the penetration depth of the weld bead for some examples. Note that in some examples, the toe of the steady portion of the weld bead on the side of the second steel plate did not have a wavy shape. For such examples, Y and Y / tL are indicated as "-".

[0092] Furthermore, the weld beads of the arc-welded joints were subjected to X-ray photography to measure the porosity defect rate in the steady portion of the weld beads. The porosity defect rate is also shown in Table 2.

[0093]

[0094]

[0095]

[0096] In Comparative Example 4, the width w of the weld bead and the thickness tL of the second steel plate did not satisfy the relationship 3.3≦w / tL≦7.0. Therefore, in Comparative Example 4, the porosity defect rate was not suppressed.

[0097] In Comparative Examples 6 and 7, weaving welding was not performed, and the droplet transfer frequency D from the torch to the molten pool and the oscillation frequency f did not satisfy the relationship D / f ≥ 25. Therefore, in Comparative Examples 6 and 7, the porosity defect rate was not suppressed.

[0098] In Comparative Example 10, the droplet transfer frequency D from the torch to the molten pool and the oscillation frequency f did not satisfy the relationship D / f≧25. Therefore, in Comparative Examples 6 and 7, the porosity defect rate was not suppressed.

[0099] In Comparative Example 12, weaving 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 3.3≦w / tL≦7.0. Therefore, in Comparative Example 12, the porosity defect rate was not suppressed.

[0100] In Comparative Example 13, the wavelength y of the torch waviness and the thickness tL of the second steel plate did not satisfy the relationship y / tL≦2.8. Therefore, in Comparative Example 13, the porosity defect rate was not suppressed.

[0101] On the other hand, in all examples where the welding conditions were appropriate, the porosity defect rate was suppressed to less than 10%. In Example 9, the wavelength y of the torch waviness was small, so the shape of the toe of the weld bead was not wavy. Therefore, in Table 1B, the wavelength Y of the toe of Example 9 is entered as "-". However, even in Example 9, the effect of suppressing porosity defects was sufficiently obtained. In the other examples, the wavelength y of the torch waviness and the wavelength Y of the toe were generally the same.

[0102] In the examples in which the Si content of the weld bead was 0.5 mass% or less, porosity defects were further suppressed. The porosity defect rate of Example 8, in which 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, in which the Si content of the weld bead was 0.5 mass% or less, were all lower than that of Example 8.

[0103] REFERENCE SIGNS LIST 1 arc welded joint 11 first steel plate 111 end 12 second steel plate 121 arc welded surface 13 weld bead 131 steady portion 1311 toe 132 starting portion 133 ending portion 13P molten pool 14 zinc-based coating 14v zinc vapor 21 first steel plate portion 22 second steel plate portion A torch AW welding wire d droplet D droplet transfer frequency pd porosity R root C gap tL plate thickness of second steel plate WD welding direction w width of weld bead x torch oscillation amplitude y wavelength of torch waviness

Claims

1. Stacking the first steel plate and the 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; forming a weld bead by arc welding the end of the first steel plate and the surface of the second steel plate that are overlapped; The surface of the second steel plate has a zinc-based plating; The arc welding is a weaving arc welding in which a torch is periodically oscillated in a direction transverse to a welding direction, The plate thickness tL (mm) of the second steel plate and the wavelength y (mm) of the waviness of the torch in the weaving arc welding are set to values ​​that satisfy 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, In the weaving arc welding, the droplet transfer frequency D (times / second) from the torch to the molten pool and the oscillation frequency f (Hz) are set to values ​​that satisfy D / f≧25. A method for manufacturing arc welded joints.

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

3. 3. The method for manufacturing an arc welded joint according to claim 1, wherein a wavelength y of the torch waviness and the plate thickness tL of the second steel plate are set to values ​​that satisfy 0.7≦y / tL.

4. The method for manufacturing an arc welded joint according to claim 1 or 2, characterized in that the weld bead does not penetrate the second steel plate in the plate thickness direction.

5. 3. The method for manufacturing an arc welded joint according to claim 1, wherein an outer edge of the weld bead intersects with mating surfaces of the first steel plate and the second steel plate in a cross section along the plate thickness direction.

6. The method for manufacturing an arc welded joint according to claim 1 or 2, wherein the oscillation frequency f is less than 10 Hz.

7. The method for manufacturing an arc welded joint according to claim 1 or 2, wherein the arc welding is Metal Active Gas welding.

8. A first steel plate portion; A second steel plate portion overlapped with the first steel plate portion in a plate thickness direction; a weld bead that joins an end of the first steel plate portion disposed on a surface of the second steel plate portion and the surface of the second steel plate portion; Equipped with a zinc-based plating is applied to 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 plate thickness tL of the second steel plate portion satisfy 3.3≦w / tL≦7.0, The porosity rate in the stationary portion of the weld bead is less than 10%. Arc welded joint.

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

10. In the stationary portion of the weld bead, a toe on the side of the second steel plate portion has a wavy shape, The wavelength Y of the toe and the plate thickness tL of the second steel plate portion satisfy 0.7≦Y / tL≦2.

8.

10. The arc welded joint according to claim 8 or 9.

11. The arc welded joint according to claim 8 or claim 9, wherein the weld bead does not penetrate the second steel plate portion in the plate thickness direction.

12. 10. The arc welded joint according to claim 8 or claim 9, characterized in that, in a cross section along the plate thickness direction, an outer edge of the weld bead intersects with a mating surface of the first steel plate portion and the second steel plate portion.

13. An automobile component comprising the arc welded joint according to claim 8 or 9.