TW201841706A - Method of arc welding hot-dip galvanized steel plate and method of producing welded member - Google Patents

Abstract

Provided are an arc welding method for a hot-dip galvanized steel sheet and a method for manufacturing welded members through which exceptional appearance of welded parts and welding strength are achieved. An arc welding method for welding together hot-dip galvanized steel sheets using a pulse arc in which an arc is generated by alternatingly supplying a peak current and a base current, wherein the method includes a step for jetting a mixed gas of Ar and CO2 as a shield gas, and a step for generating the pulse arc in a period that is set in accordance with the CO2 concentration in the shield gas.

Description

Arc welding method for plating molten zinc-based steel sheet and method for manufacturing welded member

The present invention relates to an arc welding method for depositing a molten zinc-based steel sheet and a method of manufacturing the welded member.

The molten zinc-plated (Zn)-based steel sheet is widely used for construction parts or automobile parts because of its excellent corrosion resistance. Among them, a molten zinc (Zn)-aluminum (Al)-magnesium (Mg) steel sheet containing 1% by mass or more of aluminum (Al) can maintain good corrosion resistance over a long period of time, and therefore, it is used as a substitute for the conventional molten zinc-based steel sheet. The material increases its demand. In addition, the aluminum concentration in the plating layer of the conventional molten zinc-based steel sheet is usually 0.3% by mass or less (refer to Japanese Industrial Standard JIS G3302).

When a molten zinc-based steel sheet is used for building parts or automobile parts, it is often assembled by an arc welding (arc welding) method. However, when the molten zinc-plated steel sheet is subjected to arc welding, splashes, pits, and air bubbles are usually generated (hereinafter, the bubble means that the cavity is included unless otherwise specified), and the arc welding property is inferior. This is because the boiling point of zinc (906 ° C) is lower than that of iron (Fe) (about 1538 ° C), and zinc vapor is generated during arc welding to make the arc unstable, so that splashing and bubbles are easily generated. . Further, the splash refers to a steel scrap or a weld residue such as a metal pellet which is scattered during welding. Bubbles refer to the pores contained in the beads. The bead refers to a portion of the molten metal (the interfabricated portion of the base material and the fusing metal) which is melted and solidified after being cooled, and which is a welded metal which is bonded to each other in a metallurgical manner by the welded material. Further, the recess means a depression formed by the pores appearing on the surface of the bead.

When the splash adheres to the plated surface of the molten zinc-based steel sheet, the appearance of the welded portion is not impaired, and the portion to which the splash adheres is the starting point of corrosion. Therefore, if a large amount of spatter is attached, there is a problem that the corrosion resistance is remarkably lowered. In addition, it is also necessary to remove the splash process by a wire brush or the like to increase the cost. On the other hand, if the occurrence of bubbles is remarkable, there is a problem that the welding strength is lowered.

In particular, in the case of a member requiring long-term durability, a thick-plated molten zinc-based steel sheet having a plating adhesion amount of 90 g/m ² or more per one surface is used, but the amount of plating adhesion per one surface is increased. The more the amount of zinc vapor is when the arc is welded, the more the splash and the occurrence of bubbles occur.

In addition, in the present specification, the amount of plating adhesion per one side of the molten zinc-based steel sheet is "thin-plated", and the amount of plating adhesion is "thick-plated". To record it.

As a method of suppressing generation of spatter and bubbles when welding a molten zinc-based steel sheet, a pulse arc welding method using a weld line (wire) as an electrode has been proposed. According to this pulse arc welding method, the droplet transfer from the weld line as the electrode to the base material can be suppressed from being a spray transfer, and the droplet is a small particle, and the splash is suppressed. Further, the molten pool (the portion of the bead before solidification) is stirred by the pulse arc, and at the same time, the molten pool is pressed downward, and the molten pool is thinned to promote the discharge of the zinc vapor to suppress the generation of bubbles.

For example, Patent Documents 1 and 2 disclose a pulse arc welding method in which a weld line is composed, and pulse waveforms such as a peak current, a peak period, and a frequency number are controlled within an appropriate range to suppress spatter.

[PRIOR ART DOCUMENT] [Patent Document 1] Japanese Laid-Open Patent Publication No. Hei 9-206984 (published on August 12, 1997) [Patent Document 2] JP-A-2013-184216 (September 19, 2013) Open day)

[Problems to be Solved by the Invention] However, in Patent Documents 1 and 2, only the examples of the thin plated molten steel plate having a plating adhesion amount of 45 g/m ² per one surface are disclosed, and the thick plating type is not described. A method of suppressing spatter and bubbles in a molten zinc-based steel sheet.

As described above, the more the plating adhesion amount of the molten zinc-based steel sheet, the better the corrosion resistance, but splashing and air bubbles are remarkably generated during arc welding, and the appearance of the welded portion and the welding strength are lowered. In view of the circumstances, the present invention provides an arc welding method for depositing a molten zinc-based steel sheet and a method for producing a welded member. Even if the molten zinc-based steel sheet is of a thick plating type, spatter and bubbles can be suppressed in arc welding. Produced to have a good weld appearance and weld strength.

[Means for Solving the Problem] As a result of detailed investigation, the inventors of the present invention obtained the following findings by performing arc welding using a pulse arc welding method in arc welding of a molten zinc-based steel sheet. That is, the pulse period is appropriately set in accordance with the concentration of carbon dioxide (CO ₂ ) in the shielding gas, thereby suppressing arc instability (difficult to perform injection transition) while preventing short-circuiting of the front end of the weld line and the molten pool. Therefore, new insights have been obtained: the plating amount of the plated molten zinc-based steel sheet can suppress the generation of splashes and bubbles from the thin plating type to the thick plating type. The present invention has thus been further completed based on this finding.

That is, an arc welding method for a molten zinc-based steel sheet according to an aspect of the present invention is to weld a molten zinc-based steel sheet by a pulse arc welding method in which a peak current and a base current are alternately supplied to generate an arc. Each of them includes a process in which a mixed gas of argon (Ar) plus carbon dioxide (CO ₂ ) is sprayed as a shielding gas; and a pulsed arc is generated in a cycle set according to the concentration of carbon dioxide in the shielding gas.

Further, in the arc welding method of the molten zinc-based steel sheet according to an aspect of the present invention, it is preferable that the welding target is formed in the contact portion of the molten zinc-based steel sheet which is the same as the welding target from the tip end of the welding line. The distance between the portions is such that the weld line and the molten pool generated in the contact portion are not short-circuited to each other, and the length at which the arc is not extinguished is the same as the molten zinc-based steel sheets.

Further, in the arc welding method of the molten zinc-based steel sheet according to an aspect of the present invention, it is preferable that the carbon dioxide (CO ₂ ) concentration is 5 vol% or more and 30 vol% or less, and the period of the pulse arc is adjusted to Within the range shown by the following formula (1).

1≦f≦-0.4C _C02 +22 ・(1) Here, f: pulse period Cco ₂ : carbon dioxide concentration (% by volume) in the shielding gas, and in addition, the molten zinc plating in one aspect of the present invention In the arc welding method of the steel sheet, the distance from the tip end of the weld line to the welding target is preferably 2 mm or more and 20 mm or less.

Further, in the arc welding method of the molten zinc-based steel sheet according to an aspect of the present invention, it is preferable that the peak current is 350 A or more and 650 A or less.

Further, in the arc welding method of the molten zinc-based steel sheet according to the aspect of the invention, the plating layer of the molten zinc-based steel sheet may be composed mainly of zinc and contains 1.0% by mass or more and 22.0% by mass or less. aluminum.

Further, in the arc welding method of the molten zinc-based steel sheet according to the aspect of the invention, the plating layer of the molten zinc-based steel sheet may contain 0.05% by mass or more and 10.0% by mass or less of magnesium.

Further, in the arc welding method of the molten zinc-based steel sheet in one aspect of the present invention, the plating layer of the molten zinc-based steel sheet may have a composition satisfying one or more of the following groups: 0.002 -0.1% by mass of titanium (Ti), 0.001 to 0.05% by mass of boron (B), 0 to 2.0% by mass of cerium (Si), and 0 to 2.5% by mass of iron (Fe).

Further, the arc welding method of the molten zinc-based steel sheet according to one aspect of the present invention can be subjected to arc welding in such a manner that the bubble occupancy ratio Br represented by the following formula (2) is 30% or less and is centered on the bead. The number of splashes in the area of 100 mm long and 100 mm wide is 20 or less.

Br = (Σdi / L) × 100 ・ (2) (here, di: the length of the i-th bubble observed in the bead L: the length of the bead).

In a method of manufacturing a welded component according to an aspect of the present invention, a molten zinc-based steel sheet is welded to each other by a pulse arc welding method, and a plating amount per one side of the molten zinc-based steel sheet is applied. When the pressure is 15 g/m ² or more and 250 g/m ² or less, the manufacturing method includes the following processes: a mixed gas of argon gas and carbon dioxide is sprayed as a shielding gas; and a pulse arc is generated at a cycle set by the concentration of carbon dioxide in the shielding gas. . In the contact portion of the molten zinc-based steel sheet which is the target of welding, the distance between the welding target portion and the welding target portion is 2 mm or more and 20 mm or less, and the peak current of the welding current in which the pulse arc is generated is 350 A or more. 650A or less, the concentration of carbon dioxide in the shielding gas is 5% by volume or more and 30% by volume or less, and the period of the pulse arc is adjusted within the range of the following formula (1).

1≦f≦-0.4C _C02 +22 ・・・(1) (here, f: pulse period (ms) C _CO2 : CO ₂ concentration (% by volume) in the shielding gas).

[Effect of the Invention] According to an aspect of the present invention, there is provided an arc welding method for a molten zinc-based steel sheet having a good welded portion appearance and a fusion strength, and a method for producing a welded member, wherein the molten zinc-based steel sheet is thick even if The plating type also suppresses splashes and bubbles when the arc is welded.

The following describes the embodiment of the invention. In addition, the following description is only intended to fully understand the gist of the present invention, and the present invention is not limited thereto unless otherwise specified. In addition, in this specification, "A-B" means the meaning of A or more B or less.

In the following description, in order to make it easy to understand the arc welding method of the molten zinc-based steel sheet in the embodiment of the present invention, first, an outline of a general pulse arc welding method will be described with reference to FIGS. 1 and 2 . The principle of pulse arc welding in the embodiment of the present invention is the same as the principle of the general pulse arc welding method.

Fig. 1 is a schematic view showing a pulse current waveform in a pulse arc welding method. As shown in FIG. 1, the pulse arc welding method is an arc welding method in which the peak current IP and the base current IB are alternately supplied alternately, and the peak current IP is set to be equal to or higher than the critical current of the droplet injection transition. The peak current IP flow time is set to the peak period PP, and the pulse period of the pulse current composed of the peak current IP and the base current IB is set to the period f. When the peak current IP is set to be equal to or higher than the critical current, an effect (electromagnetic contraction effect) of shrinking the tip of the wire based on the electromagnetic force is generated. Based on this electromagnetic contraction effect, the droplets at the front end of the weld line are contracted, so that the droplets are smallly granulated, and regular droplet transfer (jet transition) is performed every cycle. Thereby, the droplets smoothly transition into the molten pool, suppressing the generation of splash.

Fig. 2 is a schematic cross-sectional view showing the phenomenon of pulse arc welding. Here, the lap joint is used as a fillet joint as an example. As shown in Fig. 2, in the pulse arc welding method in which the peak current value is appropriately set, since the droplet 5 of the small particles is ejected from the weld line 2 to the molten pool 3, it is difficult to cause a short circuit. Further, the pulse arc 4 causes the molten pool 3 directly under the arc to be pressed down, and the depth of the molten pool is attenuated, thereby promoting the discharge of the zinc vapor and suppressing the generation of splashes and bubbles. The portion of the molten pool 3 that has cooled and solidified becomes the bead 6.

Further, in the pulse arc welding method, if the distance between the front end of the weld line 2 and the molten pool 3, that is, the shorter the arc length, the effect of the molten pool depression due to the pulse arc 4 is greater, thereby promoting zinc. The discharge of steam. However, if the arc length is too short, the front end of the weld line 2 is short-circuited with the molten pool 3 to generate a spark, which causes a large amount of splash. In particular, when the molten zinc-based steel sheet is of a thick plating type, since the amount of generation of zinc vapor is increased, even if the pulse arc welding method is used, the zinc vapor from the molten pool 3 is not completely released and stagnated in the molten pool 3, and The stagnant zinc vapor is sprayed out of the beat pool 3 in a single breath, so that the front end of the weld line 2 is short-circuited with the molten pool 3, resulting in significant splashing.

Therefore, the present invention prevents the short-circuit of the tip end of the weld line 2 and the molten pool 3, and the arc is unstable; even if the molten zinc-based steel sheet is of a thick plating type, the influence of the zinc vapor can be suppressed, the droplet transfer can be stabilized, and the splash can be suppressed. The generation of bubbles.

In the pulse arc welding method, argon gas and carbon dioxide gas are used as a shielding gas in order to make a droplet transition. Carbon dioxide is separated into carbon monoxide, oxygen, and the like in an arc plasma. Since this separation reaction is an endothermic reaction, the separation based on carbon dioxide causes the pulse arc 4 to cool and contract. If the contraction of the pulse arc 4 becomes excessively large, it is difficult for the droplet to perform the jet transition, and splashing is likely to occur. Further, when the contraction of the pulse 4 is excessively large, the arc force is small, and the stirring effect due to the depression of the molten pool 3 is weakened, so that it is difficult for the zinc vapor to be discharged from the molten pool 3 to generate bubbles. Therefore, in the pulse welding, the carbon dioxide in the shielding gas is usually set to 20% by volume or less.

On the other hand, when the concentration of carbon dioxide in the shielding gas is lowered, the pulse arc 4 is widened, the arc force is weakened, the penetration of the molten portion becomes shallow, the joint strength is lowered, and the expensive argon ratio is increased and welded. The problem of higher costs. In this way, although the concentration of carbon dioxide in the shielding gas is preferably high in terms of joint strength and welding cost, if the concentration of carbon dioxide in the shielding gas is increased, splashing and bubble increase are caused as described above.

The inventors of the present invention have made efforts to carry out the research, and have completed the present invention by appropriately setting the pulse period f in accordance with the concentration of carbon dioxide in the shielding gas, thereby suppressing the case where the droplets are difficult to perform the ejection transition, and further preventing the welding. The short circuit of the front end of the wire 2 and the molten pool 3 suppresses the generation of splashes and bubbles.

That is, an arc welding method for a molten zinc-based steel sheet according to an aspect of the present invention is to weld a molten zinc-based steel sheet by a pulse arc welding method in which a peak current and a base current are alternately supplied to generate an arc. Each of them includes a process in which a mixed gas of argon (Ar) and carbon dioxide (CO ₂ ) is sprayed as a shielding gas; and a pulse arc is generated in a cycle set according to a concentration of carbon dioxide in the shielding gas.

In the process of discharging the mixed gas of argon gas and carbon dioxide, a known device can be used as long as it can control the concentration of carbon dioxide in the mixed gas of argon gas and carbon dioxide. The concentration of carbon dioxide in the mixed gas of argon gas and carbon dioxide can be, for example, the concentration of carbon dioxide in the cylinder filled with the mixed gas. Further, argon gas and carbon dioxide supplied from individual cylinders may be mixed and used. In this case, the concentration of carbon dioxide in the mixed gas of the argon gas and the carbon dioxide may be determined based on the flow rate ratio, and the carbon dioxide concentration can be easily adjusted so as to change the flow rate ratio. In the Metal Active-Gas Welding (MAG Welding), a welding torch is generally used to spray a mixed gas of argon gas and carbon dioxide to the periphery of the welded portion.

In the process of generating a pulsed arc based on the period f set by the concentration of carbon dioxide in the shielding gas, as will be described later in detail, the period f is set as follows. In other words, the inventors of the present invention have obtained a new knowledge that the occurrence of spatter and bubbles can be suppressed under the conditions in which various welding conditions other than the carbon dioxide concentration and the period f are fixed, and the period f and the range of the CO ₂ concentration in the shielding gas are obtained. The period f can be set by the range thus obtained (refer to FIG. 4 for a specific example). Under the conditions of the carbon dioxide concentration and the period f outside the range, the arc is liable to become unstable, and the tip end of the weld line 2 and the molten pool 3 are easily short-circuited.

Then, by setting the period f and the concentration of carbon dioxide in the shielding gas within the obtained range, the following effects are obtained. As described above, the concentration of carbon dioxide in the shielding gas is preferably high due to the joint strength and the welding cost. However, when the concentration of carbon dioxide is high, the arcing force of the pulse arc 4 is weakened, so that the stirring effect caused by the depression of the molten pool 3 becomes small. According to the arc welding method of the present embodiment, the pulse period is set to be short in order to increase the concentration of carbon dioxide, whereby the number of times of depression of the molten pool 3 by the pulse arc 4 is increased, and the discharge of zinc vapor from the molten pool 3 can be promoted. Therefore, even if the molten zinc-based steel sheet is of a thick plating type, splashing and generation of bubbles can be suppressed. Further, according to the arc welding method of the present embodiment, the concentration of carbon dioxide in the shielding gas can be increased, thereby reducing the manufacturing cost of the welded member having good joint strength.

The present embodiment will be described in detail below.

Here, in order to appropriately set the pulse period in accordance with the concentration of carbon dioxide in the shielding gas, in the present embodiment, the position of the contact portion between the weld line and the molten zinc-coated steel sheet before welding is set. The relationship is as follows. Further, the arc welding method in one aspect of the present invention is not limited to the specific one described below, and may be, for example, the following. That is, based on various conditions, the ideal positional relationship (distance value range) of the contact portions between the weld line and the molten zinc-coated steel sheet before welding is determined, and the pulse period and the shielding gas are obtained under the conditions of the specification. The range of carbon dioxide concentrations in the medium. Based on this, the range can be determined, and the pulse period is appropriately set in accordance with the concentration of carbon dioxide in the shielding gas.

[The positional relationship between the weld line and the contact portion between the molten zinc-based steel sheets before welding] The arc welding method of the molten zinc-based steel sheet in the present embodiment will be described with reference to Fig. 3, in which the weld line and The positional relationship between the contact portions of the molten zinc-based steel sheets before welding is also the same.

Fig. 3 (a) is a method of arc welding of a molten zinc-based steel sheet in the present embodiment, in which the weld line 2 and the same molten zinc-based steel sheet 1, 1' are mutually welded in accordance with the fillet welding of the lap joint. A schematic cross-sectional view of the positional relationship of the contact portion 7; FIG. 3(b) is a cross-sectional welding of the T-joint, and the contact portion 7 of the molten zinc-based steel sheet 1, 1' is bonded to each other. A schematic diagram of the profile of the positional relationship. 3(a) and 3(b) each show a cross section in the vertical direction of the welding direction, and shows a state before welding.

As shown in Fig. 3 (a) and (b), the molten zinc-based steel sheet 1 and the molten zinc-based steel sheet 1' to be welded may be arranged in various joint shapes before welding. Figure 3 (a) is configured as a lap joint; Figure 3 (b) is configured as a T-joint. Between the galvannealed steel plate 1 and the galvannealed steel plate 1' which are disposed, a contact portion 7 which is a contact surface in contact with each other is formed. Here, in the contact portion 7, the end portion closest to the front end of the weld line 2 is referred to as a corner portion 7a. The corner portion 7a is a portion where the bead 6 (see Fig. 5) is formed adjacent to the molten zinc-based steel sheet 1 and the molten zinc-based steel sheet 1'. More specifically, in the case of the lap joint, the corner portion 7a is a flat surface including the side surface of the end portion of the molten zinc-based steel sheet 1 ′ disposed on the top surface of the molten zinc-based steel sheet 1 and the top surface The part that is crossed. In the case of the T-joint, the corner portion 7a is a plated molten zinc-based 1' which is erected on the top surface of the molten zinc-based steel sheet 1 and includes a plane having a width range which is slightly perpendicular to the top surface, and the top portion The part that intersects.

In other words, the corner portion 7a is a joint shape in which the molten zinc-based steel sheet 1 and the molten zinc-based steel sheet 1' are arranged in an arbitrary shape, and the molten zinc-based steel sheet 1 and the molten zinc-based steel sheet 1' are welded and arc-irradiated. The part can also be called the welding target part. In the case where the joint shape is a butt joint, the portion to be welded refers to the opposite side of the end portion of the molten zinc-based steel sheet 1 and the end portion of the molten zinc-based steel sheet 1', and the side of the weld line 2 Edge (ridge line).

As described above, it is important to suppress the occurrence of spatter caused by the short circuit between the front end of the weld line 2 and the molten pool 3, and to control the arc length within the appropriate range. However, referring again to FIG. 2, the molten pool 3 is oscillated up and down in a short time in synchronization with the waveform of the pulse arc 4 due to the pressing effect by the pulse arc 4, so the length of the arc in the welding is controlled and controlled. It is difficult. Therefore, in the present specification, as shown in Figs. 3(a) and 3(b), the wire front end portion 2a at the tip end of the weld line 2a is welded to the contact portion 7 of the molten zinc-plated steel sheet before welding. The distance of the corner portion 7a on the line 2 side is defined as the distance D. In the arc welding method of the present embodiment, the distance D is set to a length in which the weld line 2 and the molten pool 3 are not short-circuited to each other, and is a length in which the arc 4 does not extinguish.

Here, for example, when the arc welding is performed in the joint shape shown in FIGS. 3(a) and 3(b), the weld line 2 moves in a direction perpendicular to the paper surface, and the welded target portion is sequentially welded. Therefore, the distance D indicates that the length of the vertical line is drawn from the point of the line end portion 2a toward the welding target portion (the corner portion 7a or the edge of the weld line 2 side). Further, the straight line passing through the central axis of the weld line 2 does not necessarily need to pass through the corner portion 7a as long as the straight line passes through the vicinity of the corner portion 7a. Therefore, in a broad sense, the distance D is (i) a straight line passing through the central axis of the weld line 2, and a point of intersection with the molten zinc-based steel sheet 1 or the molten zinc-based steel sheet 1' (welding target portion); and (ii) line The distance between the front end portions 2a.

In this manner, in the arc welding method of the molten zinc-based steel sheet according to the present embodiment, the distance D from the line front end portion 2a to the corner portion 7a is maintained at a length that the weld line 2 and the molten pool 3 are not short-circuited with each other, and The welding is performed at a length where the arc does not extinguish. This method does not detect the arc length itself, but performs welding while maintaining the distance D.

Thereby, even if the plated molten steel plate is of a thick plating type, splashing and generation of bubbles can be suppressed in the arc welding.

In the arc welding method of the molten zinc-based steel sheet according to the present embodiment, it is preferable to set the distance D from the line front end portion 2a to the corner portion 7a to be in the range of 2 to 20 mm. If the distance D is less than 2 mm, the weld line 2 is short-circuited with the molten pool 3 to cause splashing. If a splash occurs, the agitation caused by the depression of the molten pool 3 does not occur, and the zinc vapor is not discharged, and bubbles are generated. On the other hand, if the distance D exceeds 20 mm, the arc is extinguished, and so-called arc suppression occurs. If the arc extinguishing occurs, the weld line 2 is short-circuited with the molten pool 3, and the pulse arc 4 generates a spark when the arc is again, and the splash pool 3 generates a splash. Further, the pulse arc 4 does not cause agitation due to the pressing during the extinguishing, so that the zinc vapor is not discharged, and bubbles are generated. Further, when the distance D exceeds 20 mm, the arc becomes wider, and the contraction effect by the electromagnetic force becomes weak. Therefore, the droplet 5 is difficult to be cut, and as a result, the droplet 5 is coarsened and floated, and splashing of large particles occurs.

The method of setting the distance D from the line front end portion 2a to the corner portion 7a in the range of 2 to 20 mm in this manner can be easily achieved by appropriately setting the pulse period in accordance with the concentration of carbon dioxide in the shielding gas as will be described later. By setting the distance D to a range of 2 to 20 mm, it is possible to effectively suppress spatter and bubble generation even if the molten zinc-based steel sheet is of a thick plating type.

In addition, the arc welding method in one aspect of the present invention may include: a position setting process, and the distance D is set such that the weld line 2 and the molten pool 3 are not shorted to each other before the welding is performed on the molten zinc-based steel sheets. The length, and the length of the arc will not go out. Then, in the welding process in which the molten zinc-plated steel sheets are welded together, the distance D is maintained and welded. The means for controlling the positional relationship between the line front end portion 2a and the corner portion 7a and controlling the distance D is not particularly limited, and a known device can be used.

[Cyclic acid concentration in the cycle and the shielding gas] In the pulsed MAG welding method, a mixed gas of argon gas and carbon dioxide for causing the droplet to be injected as a jet is used as a shielding gas. Arc welding method aspect of the present invention comprises the following processes: the discharge argon (Ar) together with a mixed gas of carbon dioxide (CO ₂₎ as the protective gas; carbon dioxide concentration and in accordance with the protective gas and the set period A pulsed arc is generated.

4 shows the relationship between the concentration (% by volume) of carbon dioxide in the shielding gas and the period f (ms), and the bubble occupancy rate and the amount of splash adhesion. The ○ mark in the figure is a case where the following two conditions are satisfied: the bubble occupancy rate is 30% or less, and the amount of splash adhesion is 20 or less. The × mark in the figure is a case where the bubble occupancy rate exceeds 30%, or the number of splash adhesions exceeds 20. The ● mark in the figure is the case where the weld bead is raised.

The range of the solid coil in FIG. 4, that is, the carbon dioxide concentration C _C02 in the shielding gas is 5 to 30% by volume, and the period f is within a specific range (within the range of the formula (1) described later), in which the bubble and the splash are suppressed. Produced, the bead shape is good. However, in the case where the carbon dioxide concentration C _C02 in the shielding gas is less than 5% by volume, the pulse arc 4 is unstable, and the beading phenomenon causes the appearance of the bead to be significantly deteriorated due to the bulging phenomenon. In addition, the generation of bubbles and splashes becomes apparent. When carbon dioxide is C _C02 than 30% by volume, it does not produce droplet ejection transition becomes short circuiting transfer, thus significantly splashes and bubbles.

Here, if the pulse period is shortened, the number of times the molten pool 3 is pressed down by the pulse arc 4 is increased, thereby promoting the discharge of the zinc vapor. However, if the period f is too short and less than 1 ms, and the supply speed of the weld line 2 is 3 m/min or less, the weld line 2 is excessively melted, and the distance from the front end of the weld line 2 to the molten pool 3 becomes long, and arc suppression or droplet formation occurs. 5 coarsening. Thereby, the droplet transition becomes unstable and spatter is generated. Further, since the molten pool 3 is not pressed by the pulse arc 4 during the arc extinguishing, bubbles are generated.

On the other hand, if the period f is too long, the weld line 2 is insufficiently melted, and the distance from the tip end of the weld line 2 to the molten pool is too short, and the tip end of the weld line 2 is short-circuited with the molten pool 3 to cause splashing. Further, since the number of times the molten pool is pressed down by the pulse arc 4 is reduced, the zinc vapor cannot be discharged, and splashes and bubbles are generated.

Further, even if the carbon dioxide concentration C _CO2 in the shielding gas is in the range of 5 to 30% by volume, if the carbon dioxide concentration C _CO2 becomes high as described above, the pulse arc is tightened to weaken the arc force, and the molten pool 3 is depressed. The stirring effect is also reduced.

As aforesaid, the arc welding method of one aspect of the present invention is, as a protective argon gas plus a mixed gas of carbon dioxide in the carbon dioxide concentration C _CO2 to 30 vol% 5 vol% or less of the mixed gas discharged Further, it is preferable to adjust the pulse period f within the range of the following formula (1) in accordance with the carbon dioxide concentration C _CO2 to generate a pulsed arc.

_{1 ≦ f ≦ -0.4C C02 +22 ·} · · (1) thereto, f: pulse period (ms) C _co2: protection of the carbon dioxide concentration in the gas (vol%) arc welding method aspect of the present invention In the case where the carbon dioxide concentration C _CO2 is high as shown in the above formula (1), the upper limit of the period f is shortened, and the number of times of pressing of the molten pool 3 by the pulse arc 4 is increased to cause the zinc pool to be discharged from the molten pool 3. Further, it is possible to prevent short-circuiting of the tip end of the weld line 2 and the molten pool, and to extinguish the arc. Even if the molten zinc-based steel sheet is of a thick plating type, the influence of the zinc vapor can be suppressed, and the droplet transition can be stabilized, and splashing and generation of bubbles can be suppressed.

Therefore, it is possible to provide an arc welding method and a method for producing a welded member of a molten zinc-based steel sheet having a good welded portion appearance and welding strength, and it is possible to suppress spatter and bubbles during arc welding even if the molten zinc-based steel sheet is of a thick plating type. .

Next, a preferred specific example of various conditions in the arc welding method of the molten zinc-based steel sheet used in the present embodiment will be described.

[Peak Current] Preferably, the peak current IP for generating a pulse arc is set in the range of 350-650A. When the supply speed of the weld line 2 is 15 m/min, if the peak current IP is lower than 350 A, the weld line 2 may be insufficiently melted, and the weld line 2 is excessively supplied, and the wire front end portion 2a and the molten pool 3 are short-circuited. Further, if the arc force is weak, the stirring effect due to the pressing of the molten pool 3 is also weakened. On the other hand, if the peak current IP exceeds 650 A, the weld line 2 is excessively melted, and the distance D exceeds 20 mm, resulting in arc suppression or coarsening of the droplet 5.

[Joint shape] In addition to the lap joint-based fillet weld shown in Fig. 3(a) and the T-joint-based fillet weld shown in Fig. 3(b), the angle joint, the cross joint, and the lap joint The present invention is applicable to any joint shape such as a plate joint or a flare joint. Furthermore, the present invention is also applicable to butt fusion based on butt joints, corner joints, cross joints, and T-joints.

[Metal-plated molten zinc-based steel sheet] In the present embodiment, a molten zinc-based steel sheet to be welded is a molten zinc-plated steel sheet, a plated alloyed molten zinc steel sheet, a molten zinc-aluminum steel sheet, or a molten zinc-aluminum-magnesium steel sheet. A plated molten steel plate mainly composed of zinc is preferred.

Among the molten zinc-based steel sheets, the molten zinc-aluminum-magnesium steel sheet may contain 1.0 to 22.0% by mass of aluminum and 0.05 to 10.0% by mass of magnesium, and is an ideal condition because of good corrosion resistance. The occurrence of the Zn Mn (Zn ₁₁ Mg ₂ ) phase is a cause of deterioration in the appearance and corrosion resistance of the plating layer. Therefore, in order to suppress the growth thereof, 0.02-0.1% by mass of titanium can be added to the plating layer of the molten zinc-aluminum-magnesium steel sheet, 0.001 - 0.05% by mass of boron. Further, in order to suppress excessive growth of the iron-aluminum (Fe-Al) alloy layer generated on the interface between the plating plate and the plating layer, and to improve the adhesion of the plating layer during processing, it is also possible to add up to 0.2% by mass of ruthenium. .

[Amount of plating adhesion] When the amount of plating adhesion of the molten zinc-based steel sheet is small, it is disadvantageous in that the corrosion resistance and the sacrificial anti-corrosion effect of the plating surface are maintained for a long period of time. After various studies, found that the per side to the coating weight 15g / m ² or more based the more effect. On the other hand, when the plating adhesion amount per one surface exceeds 250 g/m ² , the amount of zinc vapor generated is too large, and it is difficult to suppress spatter and bubbles even by the arc welding method using the molten zinc-based steel sheet of the present embodiment. produce. Therefore, it is preferable to set the plating adhesion amount per one surface to 250 g/m ² or less.

[Fuse Wire] The weld line 2 is preferably made of Japanese Industrial Standard JIS Z3312 YGW15 or JIS Z3312 YGW16. In addition to this, a solid (welded) wire specified by JIS Z3312 or other types may be used. For example: no copper wire, coated wire, slag line, etc.

The wire diameter of the weld line 2 may be, for example, 1.2 mm in diameter, or a weld line having a diameter in the range of 0.8 to 1.6 mm may also be used.

[Wire feeding speed] Regarding the wire feeding speed, in order to prevent the melting wire 2 from being excessively melted, the distance from the tip end of the welding wire 2 to the molten pool 3 becomes long, and the arc extinguishing or the droplet 5 is coarsened, preferably 3 m/min. If the supply speed exceeds 15 m/min, the supply of the weld line 2 is excessive, and the wire front end portion 2a and the molten pool 3 are short-circuited. Therefore, the upper limit is preferably 5 m/min. The wire feed speed can be appropriately selected according to the wire diameter, the period f, and the peak current IP.

[Base current] The base current IB is preferably 10-200A. If it is less than 10A, it will easily generate arc extinguishing. If it exceeds 200A, the droplet will be easily broken.

[Arc Voltage] The arc voltage is preferably 10-100V. In the case of less than 10 V, the distance from the tip end of the weld line 2 to the molten pool 3 becomes too short, and if it exceeds 100 V, the distance from the tip end of the weld line 2 to the molten pool 3 becomes too long.

[Holding angle of the torch] It is preferable to use a torch inclination angle of 30-60° in the torch maintenance angle. In addition, the advancing or retreating angle is preferably 0-30°. The torch inclination angle, the advancing angle, or the receding angle can be selected within an appropriate range as described above depending on the welding condition of the joint shape, the welding posture, and the like.

[Target position] The target position is preferably the corner portion 7a on the side of the weld line 2 among the contact portions 7 of the molten zinc-based steel sheets before welding, but the desired purpose bead shape can be obtained. The joint strength is also not limited to the corner portion 7a.

[Milling posture, direction of progress] The welding posture and the direction of the welding are not limited. The lateral direction, the longitudinal direction, the upward direction, and the downward direction can be appropriately selected depending on the shape of the welded member or the like.

[Splicing power supply method] The welding power supply is not limited. Any method such as a direct current arc type or an alternating current arc type can be used. It can be appropriately selected in accordance with the thickness, shape, and penetration of the welded component.

[Splicing speed] The welding speed can be set to, for example, 0.4 m/min. It can be set in the range of 0.1-2 m/min with various welding conditions.

Further, in the arc welding method of the present embodiment, various welding conditions are set to the conditions within the above-described ideal range, and the above-described melting line and the molten zinc-based steel sheet are welded to each other. The ideal positional relationship of the contact. Under the above conditions, the ideal range of the carbon dioxide concentration and the period f (the solid coiling range in Fig. 4) can be obtained in the arc welding method of this embodiment.

Here, in the arc welding method according to another aspect of the present invention, in the case where various welding conditions and the positional relationship are changed, the ideal range of the carbon dioxide concentration and the period f may become different from the range shown in FIG. The scope. That is to say, it is generally difficult to specify the range in which the period f is appropriately set in accordance with the concentration of carbon dioxide in the shielding gas.

According to an aspect of the present invention, an arc welding method as follows can be provided. That is, in the arc welding method of the molten zinc-based steel sheet, various welding conditions may be required to be adjusted (experienceally) in the presence of various adjustable welding conditions. As a substitution method of this method, according to an aspect of the present invention, a useful method for fixing the carbon dioxide concentration and the welding conditions other than the period f to obtain an ideal range of the carbon dioxide concentration and the period f can be provided, and the effect can be effectively suppressed. Ideal welding conditions for splashes and bubbles.

[Bubble Occupancy Rate and Splash Adhesion Quantity] According to the molten zinc-based arc welding method of the present embodiment, spattering and generation of bubbles can be suppressed, and welding of the molten zinc-based steel sheets can be performed, and the same can be provided. A welded joint formed by welding. Evaluation of the welded member (bubble occupancy rate, amount of splash adhesion) will be described with reference to FIGS. 5 and 6 .

Fig. 5 is a plan view showing a method of detecting the bubble occupancy ratio among the welded members 10 in which the molten zinc-based steel sheets are welded to each other. As shown in Fig. 5, a weld bead 6 is formed in the welded member 10 in which the molten zinc-based steel sheet 1 and the molten zinc-based steel sheet 1' are welded, and the bead 6 has a large number of bubbles 6a. Further, the length of the bead 6 in the longitudinal direction (welding line direction) is L, and the length of the i-th bubble from the one end portion of the bead 6 is di. Here, for example, when the joint shape is a T-joint, the molten zinc-based steel sheet 1 and the molten zinc-based steel sheet 1' shown in Fig. 5 are welded three-dimensionally and vertically.

According to the Japanese design and construction manual for the thin-wall fusion joints for construction, the editorial committee for the design and construction manual of the thin-wall fusion joints for construction. The integrated value of the length di of each of the cells 6a shown in Fig. 5, that is, the length of all the cells 6a formed in the bead 6 is measured, and the measured value of the integrated value Σdi (mm) is calculated. When the bubble occupancy ratio Br calculated by the following formula (2) is 30% or less from the measured value of the integrated value Σdi (mm), it is considered that there is no problem in the welding strength.

Br = (Σdi / L) × 100 (2) Here, di: the length of the i-th bubble observed in the bead L: the length of the bead.

Fig. 6 is a plan view showing a method of detecting the amount of spatter-spray adhesion among the welded members 10 in which the molten zinc-based steel sheets are welded to each other. As shown by the broken line in Fig. 6, in the region 8 having a length of 100 mm and a width of 100 mm centering on the bead 6, if the amount of spatter adhesion is 20 or less, the splash is not conspicuous, and the influence on the corrosion resistance is small. Here, the center of the bead 6 may be the center of the region 8, and the length of 100 mm means 50 mm from the side of the bead 6 (plated molten zinc-based steel plate 1), and the other side (plated molten zinc-based steel plate 1') 50mm. At this time, for example, when the joint shape of the welding member 10 is a T-joint, the length of the region 8 of 100 mm may be 50 mm in the right-angle direction around the bead 6 . Further, a width of 100 mm means the width of the region 8 in the same direction as the longitudinal direction of the bead 6.

In the welding member 10 of the present invention, the amount of splash adhesion in the region 8 is 20 or less, and the welded appearance and corrosion resistance are good.

[Examples] Four types of molten zinc-based steel sheets shown in Table 1 were used to form a lap joint filler joint, and pulse arc welding was performed. The weld line 2 is a JIS Z3312 YGW12 having a diameter of 1.2 mm, a welding speed of 0.4/min, a bead length of 180 mm, and an overlap boundary of 30 mm.

[Table 1] Plate thickness: 3.2mm, plate width: 100mm, length: 200mm

Further, in the welding, the welding state of the portion of the corner portion 7a on the side of the weld line 2 in the contact portion 7 of the molten zinc-based steel sheet which is the same as the front end of the weld line 2 is included, and the conditions shown below are included. The photographing is performed by a high speed camera, whereby the distance D from the front end of the weld line 2 to the corner portion 7a is measured. After the pulse arc welding, the amount of spatter adhesion and the bubble occupying ratio Br were measured by the aforementioned methods.

[Photography conditions for high-speed cameras] High-speed camera: M310 for laser visualization by Nobby Tech: CAVLUX HF manufactured by Cavitra Hz Pulse wavelength: 810 nm Number of frames: 4000 frames/second

Tables 2 and 3 show the types of the molten zinc-based steel sheets, the pulse arc welding conditions, the distance D from the tip end of the weld line 2 to the corner portion 7a, and the measurement results of the amount of spatter adhesion and the bubble occupancy ratio Br.

Table 2 shows the use of a molten zinc-aluminum (6%)-magnesium (3%) steel plate as a molten zinc-based steel sheet, and investigated the type of protective gas, the peak current IP, the period f, and the change of the front end of the welded wire 2 to the corner portion 7a. The amount of splash adhesion and the bubble occupancy ratio Br in the case of distance D.

[Table 2]

As shown in the embodiment No. 1-22, when the pulse period f, the carbon dioxide concentration C _CO2 and the period f are appropriately set according to the carbon dioxide concentration C _CO2 in the shielding gas, the front end of the weld line 2 is raised to the corner portion. The distance D of 7a is a suitable condition, and the number of splashes is less than 20, and the bubble occupancy rate is less than 30. Further, it has been confirmed that an arc welding member having excellent weld portion appearance and welding strength can be obtained which suppresses generation of spatter and bubbles.

On the other hand, when the pulse period f is not set according to the carbon dioxide concentration C _CO2 in the shielding gas, any one of the carbon dioxide concentration C _CO2 and the period f is the comparative example Nos. 23, 24, 26, and 29 outside the condition range of the present invention. Among them, the occurrence of spatter and bubbles is remarkable, and an arc welding member having a good welded portion appearance and welding strength cannot be obtained.

Further, in the comparative example Nos. 25, 27, and 28 from the front end of the weld line 2 to the distance D of the corner portion 7a, or too close, the occurrence of spatter and bubbles was remarkable, and the appearance and fusion of the welded portion could not be obtained. strength.

Table 3 shows the results of investigating the amount of spatter adhesion and the bubble occupancy Br by using a molten zinc-based steel sheet having various plating compositions and adhesion amounts, and welding under various pulse arc conditions and distance D.

[table 3]

As shown in No. 30-42, in the embodiment in which the carbon dioxide concentration C _CO2 , the distance D, the peak current IP, the period f, and the plating adhesion amount are within the range specified by the present invention, any of the welded parts based on the molten zinc-based steel sheet is used. Splashes and bubbles are suppressed in the middle. In particular, in the case of No. 38-42, any of the examples of the plating adhesion amount from the thin plating type of 15 g/m ^{2 to} the thick plating type of 250 g/m ² suppressed spatter and bubbles. Therefore, it was confirmed that a molten zinc-based steel sheet arc-welding member having a good welded portion appearance and welding strength can be obtained.

On the other hand, in the comparative examples of the 43-51 of Table 3, the plating adhesion amount exceeds the upper limit of the present invention by 250 g/m ² , even if the carbon dioxide concentration C _CO2 , the distance D, the peak current IP, and the period f are within the scope of the present invention. Significantly produces zinc vapor. Therefore, it is impossible to suppress the occurrence of spatter and bubbles, and it is impossible to obtain a molten zinc-based steel sheet arc-welding member having a good welded portion appearance and welding strength.

1·1’‧‧‧Gypsum-coated zinc plate

2‧‧‧welding wire

2a‧‧‧ front end of the line

3‧‧‧ molten pool

4‧‧‧ pulse arc

5‧‧‧fusion

6‧‧‧ welding beads

6a‧‧‧ bubbles

7‧‧‧Contacts

7a‧‧‧ corner (welding part)

8‧‧‧ Area (area for calculating the number of splashes)

10‧‧‧welding parts

F‧‧ cycle

Carbon dioxide concentration C _CO2 ‧‧‧

D1, d2...di‧‧‧ (bubble) length

D‧‧‧Distance

F‧‧ cycle

L‧‧‧ (bead) length

IB‧‧‧ base current

IP‧‧‧peak current

PP‧‧‧ peak period

Fig. 1 is a schematic view showing a pulse current waveform in a pulse arc welding method. FIG. 2 is a schematic cross-sectional view showing a phenomenon of pulse arc welding. [Fig. 3] (a) In the arc welding method of the molten zinc-based steel sheet in the embodiment of the present invention, when the lap joint is used for fillet welding, the weld line and the same molten zinc-based steel sheet are in contact with each other. A schematic cross-sectional view of the positional relationship of the part; (b) A schematic cross-sectional view of the positional relationship when the corner joint is welded based on the T-joint. Fig. 4 is a graph showing the relationship between the concentration (% by volume) of carbon dioxide in the shielding gas and the period f (ms), and the relationship between the bubble occupancy rate and the amount of splash adhesion. Fig. 5 is a plan view showing a method of detecting a bubble occupying ratio among the welded members in which the molten zinc-based steel sheets are welded to each other. Fig. 6 is a plan view showing a method of detecting the amount of spatter adhesion among the welded members in which the molten zinc-based steel sheets are welded to each other.

Claims (10)

An arc welding method for depositing a molten zinc-based steel sheet, characterized in that: by a pulse arc welding method in which a peak current and a base current are alternately supplied to generate an arc, the molten zinc-based steel sheets are welded to each other, and the same The following process: a mixed gas of argon (Ar) plus carbon dioxide (CO ₂ ) is sprayed as a shielding gas; and a pulsed arc is generated in a cycle set according to the concentration of carbon dioxide in the shielding gas. The arc welding method of the molten zinc-based steel sheet according to claim 1, wherein the distance from the tip end of the weld line to the contact portion of the molten zinc-based steel sheet which is the target of fusion is welded to the target portion. It is assumed that the weld line and the molten pool generated in the contact portion are not short-circuited to each other, and the length at which the arc is not extinguished is the same as that of the molten zinc-based steel sheet. The arc welding method of the molten zinc-based steel sheet according to claim 1 or 2, wherein the carbon dioxide (CO ₂ ) concentration is 5 vol% or more and 30 vol% or less, and the period of the pulse arc is adjusted to the following In the range shown by the formula (1), 1≦f≦-0.4C _C02 +22 ・・・(1) (here, f: pulse period (ms) C _co2 : concentration of carbon dioxide (% by volume) in the shielding gas) . The arc welding method of the molten zinc-based steel sheet according to claim 2, wherein a distance from the tip end of the weld line to the welding target portion is 2 mm or more and 20 mm or less. The arc welding method of the molten zinc-based steel sheet according to 2 or 4, wherein the peak current is 350 A or more and 650 A or less. In the arc welding method of the molten zinc-based steel sheet according to the second or fourth aspect, the plating layer of the molten zinc-based steel sheet contains zinc as a main component and contains 1.0% by mass or more and 22.0% by mass or less of aluminum. The arc welding method of the molten zinc-based steel sheet according to claim 6, wherein the plating layer of the molten zinc-based steel sheet contains 0.05% by mass or more and 10.0% by mass or less of magnesium. The arc welding method of the molten zinc-based steel sheet according to claim 6, wherein the composition of the plating layer of the molten zinc-based steel sheet satisfies a condition selected from one or more of the following groups: 0.002-0.1% by mass Titanium; 0.001-0.05% by mass of boron; 0-2.0% by mass of bismuth; and 0-2.5% by mass of iron. The arc welding method of the molten zinc-based steel sheet according to 2 or 4, wherein the arc welding is performed in such a manner that the bubble occupancy ratio Br represented by the following formula (2) is 30% or less, and the bead is In the center, the number of splashes in the area of 100 mm in length and 100 mm in width is 20 or less, and Br = (Σdi / L) × 100 (2) (here, di: the i-th bubble observed in the bead) Length L: length of the bead). A method for producing a welded member, characterized in that: the molten zinc-based steel sheets are welded together by a pulse arc welding method, and the plating adhesion amount per one side of the molten zinc-based steel sheet is 15 g/m ² Above 250 g/m ² , the manufacturing method comprises the following processes: a mixed gas of argon gas plus carbon dioxide is sprayed as a shielding gas; and a pulse arc is generated according to a cycle set according to a concentration of carbon dioxide in the shielding gas, wherein The distance from the front end of the weld line to the welding target portion of the molten zinc-coated steel sheet to be welded is 2 mm or more and 20 mm or less, and the peak current of the welding current generated by the pulse arc is 350 A or more and 650 A or less. The concentration of carbon dioxide in the shielding gas is 5% by volume or more and 30% by volume or less, and the period of the pulse arc is adjusted within the range of the following formula (1), 1≦f≦-0.4C _C02 +22 ・(1) ( Here, f: pulse period (ms) C _CO2 : CO ₂ concentration (% by volume) in the shielding gas).