ARC WELDING METHOD FOR HOT-DIP GALVANIZED STEEL PLATE HAVING EXCELLENT APPEARANCE OF WELDED PART AND HIGH WELDING STRENGTH, METHOD FOR MANUFACTURING WELDING MEMBER, AND WELDING MEMBER

Abstract

Hot dip Zn-based alloy coated steel sheets (1, 1) are arc-weld in such a way that (a) a current waveform is a pulsed current waveform in which (i) a peak current and a base current alternate with each other at a pulse period of 1 ms to 50 ms and (ii) an average welding current is 100 A to 350 A and (b) an average welding voltage is 20 V to 35 V. Each of the hot dip Zn-based alloy coated steel sheets (1, 1) includes a coating layer that contains Zn as a main component and that contains Al at a concentration of 1.0% by mass to 22.0% by mass, and has a coating weight W of 15 g/m.sup.2 to 250 g/m.sup.2.

Claims

1. A method of arc-welding hot dip Zn-based alloy coated steel sheets each of which includes a coating layer that contains Zn as a main component and that contains Al at a concentration of 1.0% by mass to 22.0% by mass, each of the hot dip Zn-based alloy coated steel sheets having a coating weight W of 15 g/m.sup.2 to 250 g/m.sup.2 per surface, the hot dip Zn-based alloy coated steel sheets being arc-welded in such a way that (a) a current waveform formed by a welding current is a pulsed current waveform in which (i) a peak current and a base current alternate with each other at a pulse period of 1 ms to 50 ms and (ii) an average welding current is 100 A to 350 A and (b) an average welding voltage is 20 V to 35 V.

2. The method as set forth in claim 1, wherein the coating weight W (g/m.sup.2) of the each of the hot dip Zn-based alloy coated steel sheets and an Al concentration C.sub.Al (% by mass) of the coating layer included in the each of the hot dip Zn-based alloy coated steel sheets satisfy the following expression (1):
0.0085W+0.87C.sub.Al22(1).

3. The method as set forth in claim 1, wherein the coating layer included in the each of the hot dip Zn-based alloy coated steel sheets further contains at least one selected from the group consisting of Mg, Ti, B, Si, and Fe, the coating layer containing the Mg at a concentration of 0.05% by mass to 10.0% by mass, the Ti at a concentration of 0.002% by mass to 0.10% by mass, the B at a concentration of 0.001% by mass to 0.05% by mass, the Si at a concentration of 0% by mass to 2.0% by mass, and/or the Fe at a concentration of 0% by mass to 2.5% by mass.

4. The method as set forth in claim 1, wherein the hot dip Zn-based alloy coated steel sheets are arc-welded so that: a number of spatters adhering to a region, which has a length of 100 mm and a width of 100 mm and in which a weld bead is middled, is not more than 20; and a blowhole occupancy Br, which is calculated from the following expression (2), is not more than 30%:
Br=(di/L)100(2) where: di represents a length of the ith blowhole observed; and L represents a length of the weld bead.

5. A method of producing a welded member by arc-welding hot dip Zn-based alloy coated steel sheets each of which includes a coating layer that contains Zn as a main component and that contains Al at a concentration of 1.0% by mass to 22.0% by mass, each of the hot dip Zn-based alloy coated steel sheets having a coating weight W of 15 g/m.sup.2 to 250 g/m.sup.2 per surface, the hot dip Zn-based alloy coated steel sheets being arc-welded in such a way that (a) a current waveform formed by a welding current is a pulsed current waveform in which (i) a peak current and a base current alternate with each other at a pulse period of 1 ms to 50 ms and (ii) an average welding current is 100 A to 350 A and (b) an average welding voltage is 20 V to 35 V.

6. A welded member obtained by welding hot dip Zn-based alloy coated steel sheets each of which includes a coating layer that contains Zn as a main component and that contains Al at a concentration of 1.0% by mass to 22.0% by mass, each of the hot dip Zn-based alloy coated steel sheets having a coating weight W of 15 g/m.sup.2 to 250 g/m.sup.2 per surface, a number of spatters adhering to a region, which has a length of 100 mm and a width of 100 mm and in which a weld bead is middled, being not more than 20, a blowhole occupancy Br, which is calculated from the following expression (2), being not more than 30%:
Br=(di/L)100(2) where: di represents a length of the ith blowhole observed; and L represents a length of the weld bead.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0014] FIG. 1 is a view schematically illustrating a pulsed current waveform and a pulsed voltage waveform.

[0015] FIG. 2 is a view schematically illustrating a pulsed arc welding phenomenon.

[0016] FIG. 3 is a view for explaining (i) how to count adhering spatters and (ii) a definition of a blowhole occupancy.

[0017] FIG. 4 is a view illustrating a lower limit of a suitable Al concentration of a coating layer in accordance with an embodiment of the present invention.

[0018] FIG. 5 is a view illustrating how elements contained in the coating layer affect viscosity of Fe.

DESCRIPTION OF EMBODIMENTS

[0019] FIG. 1 schematically illustrates a current waveform and a voltage waveform observed in a pulsed arc welding method. The pulsed arc welding method is an arc welding method in which a peak current IP and a base current IB are caused to alternate with each other. The peak current IP is set to be equal to or higher than a critical current at which transfer of a small droplet, that is, spray transfer is carried out. In a case where the peak current IP is equal to or higher than the critical current, a narrow is formed in a droplet at a tip of a welding wire due to a pinch effect of electromagnetic force, so that the droplet becomes smaller and, accordingly, droplet transfer is regularly carried out for every pulse period. This ultimately suppresses generation of a spatter. In contrast, in a case where the peak current IP is equal to or lower than the critical current, the droplet transfer is irregularly carried out, and the droplet becomes larger. This causes the droplet and a molten pool to be short-circuited, and ultimately causes a spatter.

[0020] FIG. 2 schematically illustrates a welding phenomenon observed in the pulsed arc welding method. According to pulsed arc welding, a small droplet 5 is transferred from a welding wire 2 to a molten pool 3, that is, spray transfer is carried out. Therefore, no short circuiting is caused, and generation of a spatter is suppressed. Furthermore, due to a pulsed arc 4, the molten pool 3 located immediately below the pulsed arc 4 is pushed down so that the molten pool 3 becomes thin. This causes Zn vapor to be easily discharged from the molten pool 3, and ultimately suppresses generation of a blowhole.

[0021] However, in a case of a heavy-weight material having a heavy coating weight, Zn vapor is generated in a large amount. Therefore, even in a case where the pulsed arc welding method is employed, some Zn vapor does not come out of a molten pool, and remains in the molten pool. This is likely to cause a blowhole. Furthermore, in a case where the some Zn vapor remaining in the molten pool blows out from the molten pool at once, an arc is disturbed. This is likely to cause a spatter. In view of the circumstances, according to an embodiment of the present invention, by (i) controlling an average welding current, an average welding voltage, and a pulse period so as to fall within respective suitable ranges and (ii) suitably managing an Al concentration of a coating layer and a coating weight, viscosity of a molten pool is decreased so that discharge of Zn vapor is promoted and, consequently, generation of a spatter and a blowhole is suppressed.

[0022] Hot dip Zn-based alloy coated steel sheet samples were laboratorially produced. Those samples varied in coating weight per surface between 15 g/m.sup.2 and 250 g/m.sup.2. Further, while coating layers of the samples each had an Mg concentration of 3% by mass, the coating layers varied in Al concentration between 1% by mass and 22% by mass. Note that the samples each had a thickness of 3.2 mm, a width of 100 mm, and a length of 200 mm. Out of the samples, the same kind of samples were fillet-welded in the form of a lap joint so that an overlap width was 30 mm and a length of a weld bead was 180 mm. Here, a welded member made up of hot dip Zn-based alloy coated steel sheets which were joined to each other was produced by pulsed arc welding in which an average welding current was set within a range of 100 A to 350 A, an average welding voltage was set within a range of 20 V to 35 V, and the pulse period was set within a range of 1 ms to 50 ms, as appropriate. An x-ray transmissive image of an arc-welded part was captured. Thereafter, as schematically illustrated in FIG. 3, lengths dl through di of blowholes each extending along a longitudinal direction of a weld bead 6 were measured, and the lengths dl through di thus measured were accumulated so as to obtain an accumulated value di (mm). By substituting the accumulated value di into the following expression (2), an occupancy Br of the blowholes (hereinafter, referred to as a blowhole occupancy Br) was calculated. Furthermore, the number of spatters adhering to a region 7 which had a width 100 mm and a length of 100 mm and in which the weld bead 6 was middled (see a dotted line illustrated in FIG. 3) was visually determined. The region 7 was a 100-mm-square region having (i) two sides each of which was parallel to the longitudinal direction of the weld bead 6 and at a location equidistant from which the weld bead 6 was located and (ii) two sides each of which was perpendicular to the longitudinal direction of the weld bead 6.

Br=(di/L)100(2)

[0023] FIG. 4 illustrates results of studying an effect of an Al concentration of a coating layer and an effect of a coating weight on a blowhole occupancy Br and the number of adhering spatters. According to the Kenchikuyo hakuban yousetsusetsugoubu sekkei sekou manyuaru (manual for designing and implementing welded joints of constructional sheets) (editorial board of a manual for designing and implementing welded joints of constructional sheets), it is considered that there is no problem with strength of a welded part in a case where a blowhole occupancy Br is not more than 30%. Furthermore, in a case where the number of adhering spatters is not more than 20, such a spatter(s) is/are not noticeable and also hardly affect corrosion resistance. In view of the above, in FIG. 4, a case where the blowhole occupancy was not more than 30% and the number of adhering spatters was not more than 20 is plotted with a white circle, and a case where the blowhole occupancy was more than 30% and/or the number of adhering spatters was more than 20 is plotted with a black circle. In a region enclosed by four straight lines (see FIG. 4), the blowhole occupancy Br is not more than 30% and the number of adhering spatters is not more than 20. It is found that, by suitably managing the coating weight and the Al concentration, it is possible to suppress generation of a spatter and a blowhole.

[0024] That is, as illustrated in FIG. 4, it is possible to suppress generation of a spatter and a blowhole by pulsed-arc-welding hot dip Zn-based alloy coated steel sheets each of which includes a coating layer having an Al concentration of 1% by mass to 22% by mass and each of which has a coating weight of 15 g/m.sup.2 to 250 g/m.sup.2 per surface, while an average welding current is being set within a range of 100 A to 350 A, an average welding voltage is being set within a range of 20 V to 35 V, and a pulse period is being set within a range of 1 ms to 50 ms, as appropriate.

[0025] Note that it is shown in FIG. 4 that, in a case where the Al concentration C.sub.Al (% by mass) of the coating layer and the coating weight W (g/m.sup.2) satisfy C.sub.Al0.0085W+0.87, the blowhole occupancy is more than 30% and/or the number of adhering spatters is more than 20. However, it is possible to cause (i) the blowhole occupancy to be not more than 30% and (ii) the number of adhering spatters to be not more than 20, by appropriately controlling a pulsed arc welding condition(s), other than the average welding current, the average welding voltage, and the pulse period, under which the pulsed arc welding is carried out. That is, in a case where the coating weight is 15 g/m.sup.2 to 250 g/m.sup.2 and C.sub.Al0.0085W+0.87, it is necessary to control a welding speed and a composition of a shielding gas in addition to the average welding current, the average welding voltage, and the pulse period, in order to cause (i) the blowhole occupancy to be not more than 30% and (ii) the number of adhering spatters to be not more than 20. However, in a case where the coating weight is 15 g/m.sup.2 to 250 g/m.sup.2 and 0.0085W+0.87C.sub.Al, it is only necessary to control the average welding current, the average welding voltage, and the pulse period. Therefore, in order to cause (i) the blowhole occupancy to be not more than 30% and (ii) the number of adhering spatters to be not more than 20, it is preferable that 0.0085W+0.87C.sub.Al.

[0026] Pulsed arc welding conditions in accordance with an embodiment of the present invention will be described below in detail.

[0027] [Average Welding Current]

[0028] According to an embodiment of the present invention, as illustrated in FIG. 1, a current waveform is preferably a pulse waveform in which a peak current and a base current alternate with each other. Furthermore, in the pulse waveform, an average welding current IA preferably falls within a range of 100 A to 350 A. According to an embodiment of the present invention, the average welding current IA is calculated from the following expression (3).

IA=((IPTIP)+(IBTIB))/(TIP+TIB)(3)

where:

[0029] IP represents a peak current (A);

[0030] IB represents a base current (A);

[0031] TIP represents a time period (ms) of the peak current; and

[0032] TIB represents a time period (ms) of the base current.

[0033] In a case where the average welding current is less than 100 A, a sufficient amount of heat is not inputted. This causes a decrease in temperature of a molten pool and, accordingly, causes an increase in viscosity of the molten pool. As a result, Zn vapor is not easily discharged from the molten pool and part of the Zn vapor remains in the molten pool, so that a blowhole is generated. Note that a welding current is related to a rate of feeding of a welding wire. In a case where the welding current is unnecessarily increased, a droplet is oversized. This causes the droplet and the molten pool to be short-circuited, and ultimately causes a spatter. Therefore, the average welding current is preferably not more than 350 A.

[0034] [Average Welding Voltage]

[0035] According to the an embodiment of present invention, an average welding voltage EA preferably falls within a range of 20 V to 35 V. According to an embodiment of the present invention, the average welding voltage EA is calculated from the following expression (4).

EA=((EPTEP)+(EBTEB))/(TEP+TEB)(4)

[0036] where:

[0037] EP represents a peak voltage (V);

[0038] EB represents a base voltage (V);

[0039] TEP represents a time period (ms) of the peak voltage; and

[0040] TEB represents a time period (ms) of the base voltage.

[0041] In a case where the average welding voltage EA is less than 20 V, a length of an arc becomes short. This causes the droplet and the molten pool to be short-circuited, and ultimately causes a spatter. In a case where the average welding voltage is more than 35 V, an excessive amount of heat is inputted. This causes burn-through.

[0042] [Pulse Period]

[0043] A pulse period PF is set so as to fall within a range of 1 ms to 50 ms. In a case where the pulse period PF is less than 1 ms, droplet transfer becomes unstable. This causes a spatter. In a case where the pulse period PF is more than 50 ms, a time period during which the arc is not generated becomes too long. This causes an effect of pushing down the molten pool to be reduced. As a result, the Zn vapor is not easily discharged from the molten pool, so that a spatter and a blowhole are generated.

[0044] [Welding Speed]

[0045] According to an embodiment of the present invention, a welding speed is not limited in particular. The welding speed is selected as appropriate depending on thicknesses of hot dip Zn-based alloy coated steel sheets.

[0046] [Shielding Gas]

[0047] In a pulsed arc welding process, an ArCO.sub.2 mixed gas is used so that transfer of a small droplet, that is, spray transfer is carried out. Also in an embodiment of the present invention, an ArCO.sub.2 mixed gas is used as a shielding gas. An Ar-30% CO.sub.2 gas containing CO.sub.2 at a concentration of 30% by volume, an Ar-20% CO.sub.2 gas containing CO.sub.2 at a concentration of 20% by volume, an Ar-5% CO.sub.2 gas containing CO.sub.2 at a concentration of 5% by volume, which concentration is much lower than those of CO.sub.2 contained in the Ar-30% CO.sub.2 gas and the Ar-20% CO.sub.2 gas, and the like are suitably used because those gases have a great effect of suppressing generation of a spatter.

[0048] [Hot Dip Zn-Based Alloy Coated Steel Sheet]

[0049] A hot dip Zn-based alloy coated steel sheet in accordance with an embodiment of the present invention includes a coating layer which contains Zn as a main component and which contains Al at a concentration of 1.0% by mass to 22.0% by mass, and has a coating weight W of 15 g/m.sup.2 to 250 g/m.sup.2.

[0050] The coating weight W and an Al concentration C.sub.Al of the coating layer preferably satisfy the following expression (1).

0.0085W+0.87C.sub.Al22(1)

[0051] where:

[0052] W represents a coating weight (g/m.sup.2); and

[0053] C.sub.Al represents an Al concentration (% by mass) of a coating layer.

[0054] The coating layer of the hot dip Zn-based alloy coated steel sheet can further contain at least one selected from the group consisting of Mg, Ti, B, Si, and Fe. In this case, the coating layer can contain Mg at a concentration of 0.05% by mass to 10.0% by mass, Ti at a concentration of 0.002% by mass to 0.10% by mass, B at a concentration of 0.001% by mass to 0.05% by mass, Si at a concentration of 0% by mass to 2.0%, and/or Fe at a concentration of 0% by mass to 2.5% by mass.

[0055] A hot dip coating method is not limited in particular. However, in general, it is advantageous in terms of a cost to use an in-line annealing type hot dip coating machine. A composition of the coating layer substantially reflects a composition of a hot dip coating bath. Component elements contained in the coating layer will be described below. Note that % used to describe the component elements of the coating layer means % by mass unless otherwise stated.

[0056] Al is effective in improving corrosion resistance of the coated steel sheet. Furthermore, Al suppresses generation of Mg oxide-based dross in the hot dip coating bath. Moreover, as illustrated in FIG. 5, even in a case where Al is small in amount, Al has an effect of decreasing viscosity of Fe. Al contained in the coating layer is taken in the molten pool during arc welding so that the viscosity of the molten pool is decreased. This promotes discharge of the Zn vapor and, ultimately, suppresses generation of a spatter and a blowhole. In order to sufficiently exert those effects, it is necessary to ensure that the hot dip coating bath contains Al at a concentration of not less than 1.0%, more preferably not less than 4.0%. In contrast, in a case where the hot dip coating bath contains Al at a high concentration, an FeAl alloy layer, which is brittle, is likely to grow under the coating layer. Excessive growth of such an FeAl alloy layer causes a decrease in adhesion of the coating layer. As a result of various studies, the hot dip coating bath preferably contains Al at a concentration of not more than 22.0%. Alternatively, the hot dip coating bath can be each controlled so as to contain Al at a concentration of not more than 15.0% or not more than 10.0%.

[0057] Mg has an effect of uniformly producing a corrosion product on a surface of the coating layer so that the corrosion resistance of the coated steel sheet is remarkably enhanced. It is more effective that the hot dip coating bath contain Mg at a concentration of not less than 0.05%, more preferably not less than 1.0%. However, in a case where the hot dip coating bath contains Mg at a high concentration, Mg oxide-based dross is likely to be generated. Since the Mg oxide-based dross causes a reduction in quality of the coating layer, the hot dip coating bath is controlled so as to contain Mg at a concentration of not more than 10.0%. Moreover, since a boiling point of Mg is approximately 1091 C., which is lower than a melting point of Fe, Mg is vaporized during the arc welding, as with the case of Zn. It is considered that Mg vapor thus generated causes a spatter and a blowhole. Therefore, the hot dip coating bath preferably contains Mg at a concentration of not more than 10.0%.

[0058] In a case where the hot dip coating bath contains Ti, generation and growth of a Zn.sub.11Mg.sub.2-based phase, which causes the coating layer to be poor in appearance and which causes the coated steel sheet to be poor in corrosion resistance, are suppressed. Therefore, the hot dip coating bath preferably contains Ti. In a case where a concentration of Ti contained in the hot dip coating bath is less than 0.002%, such a suppressing effect is not sufficiently exerted. In a case where the concentration of Ti is more than 0.1%, the surface of the coating layer becomes poor in appearance due to generation and growth of a TiAl-based precipitate during coating. Therefore, according to an embodiment of the present invention, the concentration of Ti contained in the hot dip coating bath is limited to 0.002% to 0.1%.

[0059] As with the case of Ti, B also has an effect of suppressing generation and growth of a Zn.sub.11Mg.sub.2-based phase. In a case of B, it is more effective that the hot dip coating bath contain B at a concentration of not less than 0.001%. Note, however, that, in a case where the hot dip coating bath contains B at a high concentration, the surface of the coating layer becomes poor in appearance due to a TiB-based or AlB-based precipitate. Therefore, the hot dip coating bath is preferably controlled so as to contain B at a concentration of not more than 0.05%.

[0060] In a case where the hot dip coating bath contains Si, excessive growth of an FeAl alloy layer, which is generated at an interface between the coating layer and a surface of a base steel sheet, is suppressed. This advantageously improves workability of a hot dip ZnAlMg-based alloy coated steel sheet. Therefore, the hot dip coating bath can contain Si as necessary. In this case, it is more effective that the hot dip coating bath contain Si at a concentration of not less than 0.005%. Note, however, that, in a case where the hot dip coating bath contains Si at a high concentration, this results in an increase in amount of dross in the hot dip coating bath. Therefore, the hot dip coating bath preferably contains Si at a concentration of not more than 2.0%.

[0061] Since the base steel sheet is dipped in and caused to pass through the hot dip coating bath, Fe is likely to be mixed in the hot dip coating bath. In a case where Fe is mixed in a ZnAlMg-based coating layer, the hot dip ZnAlMg-based alloy coated steel sheet becomes poor in corrosion resistance. Therefore, the hot dip coating bath preferably contains Fe at a concentration of not more than 2.5%.

[0062] [Coating Weight]

[0063] In a case where the hot dip ZnAlMg-based alloy coated steel sheet has a light coating weight, this causes an disadvantage in maintaining corrosion resistance and a sacrificial protection effect of a coated surface of the hot dip ZnAlMg-based alloy coated steel sheet over a long time period. As a result of various studies, it is more effective that the hot dip ZnAlMg-based alloy coated steel sheet have a coating weight of not less than 15 g/m.sup.2 per surface. In a case where the coating weight is more than 250 g/m.sup.2, the Zn vapor is generated in an excessive amount, and it becomes difficult to suppress generation of a spatter and a blowhole even by the method of the present invention. Therefore, an upper limit of the coating weight is 250 g/m.sup.2.

[0064] [Blowhole Occupancy, Number of Adhering Spatters]

[0065] According to the Kenchikuyo hakuban yousetsusetsugoubu sekkei sekou manyuaru (manual for designing and implementing welded joints of constructional sheets) (editorial board of a manual for designing and implementing welded joints of constructional sheets), it is considered that there is no problem with strength of a welded part in a case where a blowhole occupancy Br, which is calculated by substituting into the following expression (2) a value di (mm) obtained by accumulating lengths of blowholes schematically illustrated in FIG. 3, is not more than 30%. A welded member in accordance with an embodiment of the present invention has a welded part which has a blowhole occupancy Br of not more than 30% and which is accordingly excellent in strength.

Br=(di/L)100(2)

[0066] where: di represents a value (mm) obtained by accumulating lengths of blowholes; and

[0067] L represents a length (mm) of a weld bead.

[0068] In a case where the number of spatters adhering to a region 7, which has a width of 100 mm and a length of 100 mm and in which a weld bead is middled (see a region enclosed by a dotted line in FIG. 3), is not more than 20, such a spatter(s) is/are not noticeable and also hardly affect corrosion resistance. According to the welded member in accordance with an embodiment of the present invention, the number of spatters is not more than 20, and, accordingly, the welded part is excellent in appearance and the welded member is excellent in corrosion resistance.

[0069] A method of arc-welding hot dip Zn-based alloy coated steel sheets in accordance with an embodiment of the present invention is a method of arc-welding hot dip Zn-based alloy coated steel sheets each of which includes a coating layer that contains Zn as a main component and that contains Al at a concentration of 1.0% by mass to 22.0% by mass and each of which has a coating weight W of 15 g/m.sup.2 to 250 g/m.sup.2, the hot dip Zn-based alloy coated steel sheets being arc-welded in such a way that (a) a current waveform formed by a welding current is a pulsed current waveform in which (i) a peak current and a base current alternate with each other at a pulse period of 1 ms to 50 ms and (ii) an average welding current is 100 A to 350 A and (b) an average welding voltage is 20 V to 35 V.

[0070] Further, the method of arc-welding hot dip Zn-based alloy coated steel sheets in accordance with an embodiment of the present invention is preferably arranged such that the coating weight W (g/m.sup.2) of the each of the hot dip Zn-based alloy coated steel sheets and an Al concentration C.sub.Al (% by mass) of the coating layer included in the each of the hot dip Zn-based alloy coated steel sheets satisfy the following expression (1):

0.0085W+0.87C.sub.Al22(1).

[0071] Further, the method of arc-welding hot dip Zn-based alloy coated steel sheets in accordance with an embodiment of the present invention can be arranged such that the coating layer included in the each of the hot dip Zn-based alloy coated steel sheets further contains at least one selected from the group consisting of Mg, Ti, B, Si, and Fe, the coating layer containing the Mg at a concentration of 0.05% by mass to 10.0% by mass, the Ti at a concentration of 0.002% by mass to 0.10% by mass, the B at a concentration of 0.001% by mass to 0.05% by mass, the Si at a concentration of 0% by mass to 2.0% by mass, and/or the Fe at a concentration of 0% by mass to 2.5% by mass.

[0072] Further, the method of arc-welding hot dip Zn-based alloy coated steel sheets in accordance with an embodiment of the present invention can be arranged such that the hot dip Zn-based alloy coated steel sheets are arc-welded so that: a number of spatters adhering to a region, which has a length of 100 mm and a width of 100 mm and in which a weld bead is middled, is not more than 20; and a blowhole occupancy Br, which is calculated from the following expression (2), is not more than 30%:

Br=(di/L)100(2)

[0073] where:

[0074] di represents a length of the ith blowhole observed; and

[0075] L represents a length of the weld bead.

[0076] A method of producing a welded member in accordance with an embodiment of the present invention is a method of producing a welded member by arc-welding hot dip Zn-based alloy coated steel sheets each of which includes a coating layer that contains Zn as a main component and that contains Al at a concentration of 1.0% by mass to 22.0% by mass, each of the hot dip Zn-based alloy coated steel sheets having a coating weight W of 15 g/m.sup.2 to 250 g/m.sup.2 per surface, the hot dip Zn-based alloy coated steel sheets being arc-welded in such a way that (a) a current waveform formed by a welding current is a pulsed current waveform in which (i) a peak current and a base current alternate with each other at a pulse period of 1 ms to 50 ms and (ii) an average welding current is 100 A to 350 A and (b) an average welding voltage is 20 V to 35 V.

[0077] A welded member in accordance with an embodiment of the present invention is a welded member obtained by welding hot dip Zn-based alloy coated steel sheets each of which includes a coating layer that contains Zn as a main component and that contains Al at a concentration of 1.0% by mass to 22.0% by mass, each of the hot dip Zn-based alloy coated steel sheets having a coating weight W of 15 g/m.sup.2 to 250 g/m.sup.2 per surface, a number of spatters adhering to a region, which has a length of 100 mm and a width of 100 mm and in which a weld bead is middled, being not more than 20, a blowhole occupancy Br being not more than 30%. The welded member has a welded part that is excellent in appearance, and is excellent in corrosion resistance.

EXAMPLES

[0078] A cold-rolled steel strip having a thickness of 3.2 mm and a width of 1000 mm was used as a base steel sheet. The cold-rolled steel strip was caused to pass through a hot dip coating line so as to produce a hot dip ZnAlMg-based alloy coated steel sheet.

[0079] Samples each having a width of 100 mm and a length of 200 mm were cut off from the hot dip ZnAlMg-based alloy coated steel sheet, and were pulsed-arc-welded so that the samples were fillet-welded in the form of a lap joint. As a solid wire, JIS Z3312 YGW12 was used. A welding speed was 0.4 m/min. A length of a welding bead was 180 mm. An overlap width was 30 mm. The other pulsed arc welding conditions are shown in Tables 1 and 2. After pulsed arc welding, an x-ray transmissive image was captured, and a blowhole occupancy Br was determined by the above-described method. Furthermore, the number of adhering spatters was visually determined.

[0080] Table 1 shows Examples in each of which pulsed arc welding in accordance with an embodiment of the present invention was carried out. Table 2 shows (i) Reference Examples in each of which an Al concentration C.sub.Al (% by mass) of a coating layer and a coating weight W (g/m.sup.2) satisfied C.sub.Al0.0085W+0.87 and (ii) Comparative Examples in each of which pulsed arc welding was carried out under a condition that an Al concentration of a coating layer was outside a range required for the present invention.

TABLE-US-00001 TABLE 1 Coating Lower limit of Al Presence or weight per concentration absence of surface (C.sub.Al = 0.0085W + 0.87) Compoisiton of coating layer (% by mass) Zn.sub.11Mg.sub.2- No. (g/m.sup.2) (% by mass) Al Mg Ti B Si Fe based phase 1 15 1.0 1.5 1.2 Present 2 46 1.3 2.1 1.1 0.098 Absent 3 60 1.4 1.8 3.1 0.006 Absent 4 88 1.6 2.8 1.2 0.87 Absent 5 118 1.9 2.1 0.1 0.09 Absent 6 188 2.5 3.2 1.3 0.004 0.003 Absent 7 245 3.0 3.6 1.1 0.003 0.047 0.11 Absent 8 42 1.2 4.2 1.0 0.004 0.002 0.91 0.02 Absent 9 87 1.6 4.1 1.2 0.008 0.021 0.08 Absent 10 114 1.8 4.5 1.2 0.091 0.01 0.11 Absent 11 189 2.5 3.8 0.9 0.023 0.01 Absent 12 243 2.9 3.9 1.1 0.093 0.045 0.12 0.03 Absent 13 30 1.1 5.8 2.9 0.013 0.019 0.22 1.22 Absent 14 57 1.4 5.8 3.1 0.054 0.006 0.23 0.33 Absent 15 97 1.7 6.1 3.3 0.078 0.002 0.99 1.23 Absent 16 132 2.0 6.3 2.9 0.043 0.047 0.89 0.11 Absent 17 178 2.4 6.0 3.0 0.055 0.045 0.09 Absent 18 245 3.0 5.8 3.2 0.058 0.011 1.89 0.10 Absent 19 58 1.4 10.9 3.0 0.045 0.008 0.12 0.23 Absent 20 93 1.7 11.0 2.9 0.098 0.023 0.09 0.18 Present 21 145 2.1 10.4 2.8 0.002 0.033 0.02 0.09 Absent 22 189 2.5 10.9 3.2 0.078 0.002 0.01 0.08 Absent 23 243 2.9 11.1 3.1 0.089 0.044 0.22 0.12 Absent 24 45 1.3 16.2 5.8 0.091 0.042 1.12 2.19 Absent 25 128 1.9 15.4 6.3 0.088 0.043 1.98 0.12 Absent 26 231 2.8 15.5 5.4 0.077 0.043 1.21 0.01 Absent 27 90 1.6 19.8 9.6 0.093 0.048 1.10 1.99 Absent 28 129 2.0 20.4 9.3 0.084 0.041 1.02 2.31 Absent 29 187 2.5 21.6 9.6 0.090 0.034 1.99 2.01 Absent 30 239 2.9 21.5 9.6 0.089 0.039 1.78 2.31 Absent Pulsed arc welding conditions Composition of Average Average shielding gas welding welding Pulse Blowhole Number of *% indicates current voltage period occupancy adhering No. % by volume (A) (V) (ms) Br (%) spatters Classification 1 Ar-5% CO.sub.2 100 20 1 5 0 Example 2 Ar-5% CO.sub.2 150 22 5 12 2 3 Ar-5% CO.sub.2 200 24 10 16 4 4 Ar-5% CO.sub.2 250 26 20 16 3 5 Ar-10% CO.sub.2 300 28 30 19 7 6 Ar-10% CO.sub.2 325 32 40 25 9 7 Ar-10% CO.sub.2 350 35 50 28 16 8 Ar-15% CO.sub.2 100 20 1 4 0 9 Ar-15% CO.sub.2 200 22 5 8 0 10 Ar-15% CO.sub.2 250 24 15 16 3 11 Ar-15% CO.sub.2 300 28 25 18 6 12 Ar-20% CO.sub.2 350 35 45 25 10 13 Ar-20% CO.sub.2 100 22 1 0 0 14 Ar-20% CO.sub.2 150 24 5 0 0 15 Ar-20% CO.sub.2 200 26 10 4 0 16 Ar-30% CO.sub.2 250 28 20 5 2 17 Ar-30% CO.sub.2 300 30 30 17 5 18 Ar-30% CO.sub.2 350 35 50 22 8 19 Ar-30% CO.sub.2 100 20 5 0 0 20 Ar-30% CO.sub.2 175 25 10 0 0 21 Ar-30% CO.sub.2 200 28 15 4 1 22 Ar-30% CO.sub.2 250 30 35 7 2 23 Ar-5% CO.sub.2 350 32 50 16 5 24 Ar-5% CO.sub.2 125 25 5 0 0 25 Ar-5% CO.sub.2 175 28 15 0 2 26 Ar-10% CO.sub.2 350 35 45 6 6 27 Ar-10% CO.sub.2 120 20 5 4 3 28 Ar-15% CO.sub.2 150 25 25 6 3 29 Ar-20% CO.sub.2 300 30 30 8 4 30 Ar-20% CO.sub.2 350 35 50 11 4

TABLE-US-00002 TABLE 2 Coating Lower limit of Al Presence or weight per concentration absence of surface (C.sub.Al = 0.0085W + 0.87) Compoisiton of coating layer (% by mass) Zn.sub.11Mg.sub.2- No. (g/m.sup.3) (% by mass) Al Mg Ti B Si Fe based phase 31 128 2.0 1.1 1.1 Present 32 145 2.1 1.4 1.2 0.002 Absent 33 191 2.5 1.6 1.1 0.006 Absent 34 248 3.0 1.8 1.2 0.01 Absent 35 34 1.2 2.1 0.1 0.02 Absent 36 98 1.7 6.0 3.3 0.005 0.003 Absent 37 245 3.0 6.6 3.1 0.015 0.047 0.11 Absent 38 46 1.3 6.2 3.0 0.098 0.021 0.08 Absent 39 87 1.6 4.1 1.2 0.004 0.002 0.91 0.02 Absent 40 289 3.3 3.5 2.2 0.091 0.01 0.02 Absent Pulsed arc welding conditions Composition of Average Average shielding gas welding welding Pulse Blowhole Number of *% indicates current voltage period occupancy adhering No. % by volume (A) (V) (ms) Br (%) spatters Classification 31 Ar-5% CO.sub.2 100 20 1 45 38 Reference 32 Ar-5% CO.sub.2 150 22 5 48 42 Example 33 Ar-5% CO.sub.2 200 24 10 66 54 34 Ar-5% CO.sub.2 250 26 20 87 64 35 Ar-10% CO.sub.2 80 20 30 39 15 Comparative 36 Ar-10% CO.sub.2 400 24 40 25 49 Example 37 Ar-10% CO.sub.2 150 18 50 28 46 38 Ar-20% CO.sub.2 125 30 0.5 24 38 39 Ar-20% CO.sub.2 200 22 75 48 54 40 Ar-20% CO.sub.2 250 26 20 58 56

[0081] As is clear from No. 1 through 30 shown in Table 1, the blowhole occupancy was not more than 30% and the number of adhering spatters was not more than 20 in each of Examples, in each of which pulsed arc welding conditions and an Al concentration of a coating layer fell within ranges required for the present invention. It is found from Examples that, by the present invention, a hot dip ZnAlMg-based alloy coated steel sheet arc-welded member is obtained which has a welded part that is excellent in appearance and strength and which is excellent in corrosion resistance.

[0082] In Reference Examples No. 31 through 34 shown in Table 2, in each of which Reference Examples the Al concentration C.sub.Al (% by mass) of the coating layer and the coating weight W (g/m.sup.2) satisfied C.sub.Al<0.0085W+0.87, generation of spatters and blowholes was observed. Note, however, that, in a case where C.sub.Al<0.0085W+0.87 is satisfied, it is possible to cause (i) the blowhole occupancy to be not more than 30% and (ii) the number of adhering spatters to be not more than 20, by appropriately controlling the pulsed arc welding conditions other than an average welding current, an average welding voltage, and a pulse period.

[0083] In contrast, in Comparative Examples No. 35 through 39, in each of which the average welding current, the average welding voltage, and the pulse period were outside the ranges required for the present invention, spatters and blowholes were excessively generated. Moreover, in Comparative Example No. 40, in which a coating weight was outside a range required for the present invention, spatters and blowholes were excessively generated.

REFERENCE SIGNS LIST

[0084] 1, 1 Hot dip Zn-based alloy coated steel sheet [0085] 2 Welding wire [0086] 3 Molten pool [0087] 4 Pulsed arc [0088] 5 Droplet [0089] 6 Weld bead [0090] 7 Region in which the number of spatters is determined