JP6080391B2 - Method for producing Zn-Al-Mg plated steel sheet arc welded structural member - Google Patents

Description

  The present invention relates to a method for producing an arc-welded structural member having excellent resistance to molten metal embrittlement cracking constituted by using a molten Zn—Al—Mg-based plated steel sheet member for one or both members to be joined.

  Since the hot dip galvanized steel sheet has good corrosion resistance, it is used in a wide range of applications including building members and automobile members. Among them, the hot-dip Zn—Al—Mg-based steel sheet maintains excellent corrosion resistance for a long period of time, and therefore, the demand is increasing as a material to replace the conventional hot-dip galvanized steel sheet.

As described in Patent Documents 1 and 2, the plated layer of the hot-dip Zn—Al—Mg-based plated steel sheet has a primary Al phase or primary Al phase in a Zn / Al / Zn ₂ Mg ternary eutectic matrix. It has a metal structure in which a Zn single phase is dispersed, and the corrosion resistance is improved by Al and Mg. Since a dense and stable corrosion product containing Mg in particular is uniformly formed on the surface of the plated layer, the corrosion resistance of the plated layer is remarkably improved as compared with the hot dip galvanized steel sheet.

  In the case of assembling building members, automobile members, and the like using a molten Zn—Al—Mg plated steel sheet, a gas shield arc welding method is often applied. When arc welding is performed on a hot-dip Zn-Al-Mg-based steel sheet, there is a problem that hot metal embrittlement cracking is likely to occur as compared with a hot-dip galvanized steel sheet. This is considered to be caused by a decrease in the liquidus temperature of the plating layer due to the Mg content (Patent Documents 3 and 4).

  When arc welding is performed on the plated steel sheet, the metal of the plating layer melts on the surface of the surrounding base material (plating original sheet) through which the arc has passed. In the case of a Zn-Al-Mg plated steel sheet, the alloy of the plating layer has a liquidus temperature lower than the melting point of Zn (about 420 ° C.) and maintains a molten state for a relatively long time. In the example of the Zn-6 mass% Al-3 mass% Mg alloy, the solidification end temperature is about 335 ° C. Molten metal derived from the Zn-Al-Mg plating layer melted on the surface of the base metal reduces the Al concentration as the Al component reacts with the underlying Fe at an early stage and is consumed as an Fe-Al alloy layer. Finally, the composition becomes close to a Zn—Mg binary system, but even with a Zn-3 mass% Mg alloy, the solidification end temperature is 360 ° C. and lower than the melting point of Zn, 420 ° C. Therefore, in the case of a Zn—Al—Mg-based plated steel sheet, the time during which the metal in the plated layer melted during arc welding stays on the surface of the base material while maintaining the liquid phase is longer than that in the galvanized steel sheet.

  When the surface of a base metal that is in a tensile stress state during cooling immediately after arc welding is exposed to molten plated metal for a long time, the molten metal penetrates into the crystal grain boundaries of the base metal and causes molten metal embrittlement cracking. It becomes a cause. When molten metal embrittlement cracking occurs, it becomes the starting point of corrosion and corrosion resistance decreases. In addition, the strength and fatigue characteristics may be reduced, causing problems.

As a method for suppressing molten metal embrittlement cracking of a molten Zn—Al—Mg-based plated steel sheet during arc welding, for example, a method of cutting and removing a plating layer before arc welding has been proposed. Patent Document 4 discloses a technique of imparting resistance to molten metal embrittlement cracking by applying a steel plate whose ferrite crystal grain boundary is reinforced by addition of B to a plating original plate. Patent Document 5 discloses a technique of suppressing molten metal embrittlement cracking by filling Zn, Al, and Mg during arc welding by filling a flux added with TiO ₂ and FeO into the outer sheath of a welding wire. .

Japanese Patent No. 3149129 Japanese Patent No. 3179401 Japanese Patent No. 4475787 Japanese Patent No. 3715220 JP 2005-230912 A

  The method of cutting and removing the plating layer and the method of using a special welding wire are accompanied by a great increase in cost. The technique of using B-added steel for the plating base plate reduces the degree of freedom in selecting the steel type. Moreover, even if these methods are adopted, molten metal embrittlement cracking may not be sufficiently prevented depending on the part shape and welding conditions, and a radical arc welding structure using a Zn-Al-Mg based steel sheet is essential. It is not a measure to prevent molten metal embrittlement cracking.

  On the other hand, in recent years, a high-tensile steel plate having a tensile strength of 590 MPa or more has been used as a plating base plate for reducing the weight of automobiles. In such a molten Zn-Al-Mg plated steel sheet using high-tensile steel sheet, the tensile stress in the weld heat-affected zone is increased, so that molten metal embrittlement cracking is likely to occur, and applicable part shapes and applications are limited. The

  In view of such a current situation, the present invention is excellent in resistance to molten metal brittleness in an arc welded structure member using a Zn-Al-Mg-based plated steel sheet member without being restricted by the steel type of the plating base plate and a significant increase in cost. It aims at providing what has fracturing ability.

According to the inventors' investigation, the plating layer disappears once by evaporation in the vicinity of the weld bead during gas shielded arc welding, but after the arc passes, the plating layer metal is in a molten state at a position slightly away from the bead. It has been confirmed that the phenomenon of immediately spreading to the above disappeared portion occurs. If this wetting spread is suppressed and cooling is completed while maintaining the state of evaporative disappearance, the penetration of the plating layer component into the base metal is avoided at a position close to the welding beat, and the molten metal embrittlement crack is It can be effectively prevented. As a result of detailed studies, the inventors have significantly reduced the concentration of CO ₂ that is usually blended in the shielding gas by about 20% by volume, whereby the above-described wetting and spreading in the Zn—Al—Mg based plated steel sheet member can be achieved. It has been found that it is significantly suppressed, and the present invention has been completed.

That is, the above object is to manufacture a welded structural member by joining steel materials by gas shielded arc welding, and at least one member to be joined is a molten Zn—Al—Mg based plated steel plate member, and Ar gas, He gas or By using a shielding gas whose CO ₂ concentration is adjusted to 0 to 7% by volume based on a mixed gas of Ar + He and using a manufacturing method of a Zn—Al—Mg-based plated steel sheet arc welded structural member having excellent resistance to molten metal embrittlement cracking Achieved.

  Here, the “molten Zn—Al—Mg-based plated steel sheet member” is a member made of a molten Zn—Al—Mg-based plated steel sheet, or a member formed by using it as a raw material.

The molten Zn—Al—Mg based steel sheet is, for example, mass%, Al: 1.0 to 22.0%, preferably 4.0 to 22.0%, Mg: 0.05 to 10.0%, Ti : 0 to 0.10%, B: 0 to 0.05%, Si: 0 to 2.0%, Fe: 0 to 2.5%, the one having a plating layer composed of the balance Zn and inevitable impurities is suitable. It becomes a target. The plating adhesion amount per one side is, for example, 20 to 250 g / m ² .

  According to the present invention, an arc welded structure using a molten Zn—Al—Mg-based plated steel sheet member that is inherently susceptible to molten metal embrittlement cracking is one that exhibits excellent resistance to molten metal embrittlement cracking. It became possible to realize stably without increasing the cost. There is no particular restriction on the steel type of the plating base plate, and it is not necessary to adopt a steel type to which a special element is added as a measure against molten metal embrittlement cracking. Even when a high-strength steel plate is applied, excellent melt metal embrittlement cracking resistance can be obtained. Moreover, the freedom degree with respect to a component shape is also large. Therefore, the present invention is widely used in a wide variety of applications including Zn-Al-Mg-plated steel sheet arc welded structural members, including automotive arc welded structural members that use high-tensile steel sheets that are expected to increase in the future. It contributes.

The figure which showed typically the cross section of the torch and base material in gas shielded arc welding. The figure which showed typically the welding part cross-section of a lap fillet welded joint. The figure which showed typically the cross-sectional state of the high temperature welded part immediately after the arc passed at the time of the arc welding of a hot-dip Zn-Al-Mg type plated steel plate. The figure which showed typically the cross-section of the conventional Zn-Al-Mg type plated steel plate arc welding structural member cooled from the state of FIG. The figure which showed typically the cross-section of the Zn-Al-Mg system plating steel plate arc welding structural member according to this invention obtained by cooling from the state of FIG. Zn-Al-Mg plated steel sheet arc welding structure plating layer evaporation zone graph showing the effect of shielding gas CO ₂ concentration on the length of the member. The figure which showed the welding experiment method for investigating the molten metal embrittlement cracking resistance.

FIG. 1 schematically shows a cross section of a torch and a base material during gas shielded arc welding. The welding torch 31 advances in the direction of the arrow while forming an arc 35 on the surface of the base material 1. A shield gas 34 is blown out from the periphery of the electrode 33 and the welding wire 32 positioned at the center of the welding torch 31 to protect the arc 35 and the surface of the base material 1 exposed to high temperatures from the atmosphere. A part of the base material 1 melted by heat input from the arc 35 is rapidly solidified after the welding torch 31 passes and forms a weld bead 2 made of weld metal. The shield gas 34 needs to be a non-oxidizing gas. In general, as the base gas an inert gas such as Ar, which Ar + CO ₂ mixed gas of CO ₂ were mixed for about 20 vol% is employed. It is considered that a part of CO ₂ in the shielding gas 34 is separated from CO and O ₂ by the plasma arc 35, and the CO exerts a reducing action to activate the surface of the base material 1 and weld beads. It is said to be responsible for suppressing oxidation in the surrounding area. CO ₂ is also considered to help stabilize the arc 35.

  FIG. 2 schematically illustrates the cross-sectional structure of the welded portion of the lap fillet weld joint. This type of welded joint by arc welding is frequently used for automobile chassis. A base material 1 and a base material 1 ′, which are steel plate members, are arranged so as to overlap each other, a weld bead 2 is formed on the surface of the base material 1 and an end surface of the base material 1 ′, and both members are joined. The broken lines in the figure represent the surface position of the base material 1 and the end face position of the base material 1 'before welding. The intersection of the base metal surface and the weld bead is called the “bead toe”. In the drawing, the bead toe portion of the base material 1 is indicated by reference numeral 3.

3 to 5 schematically show an enlarged cross-sectional structure of a portion corresponding to the vicinity of the bead toe 3 shown in FIG.
FIG. 3 schematically shows a cross-sectional state in the vicinity of a high-temperature weld immediately after the arc passes during gas shielded arc welding of a Zn—Al—Mg based steel sheet. The surface of the base material 1 was covered with a uniform plating layer 7 via the Fe-Al alloy layer 6 before welding, but the metal in the plating layer evaporated near the bead toe 3 due to the passage of the arc. And disappeared (plating layer evaporation region 9). In the portion where the distance from the bead toe 3 is larger than that, the original plating layer 7 is melted to become the Zn—Al—Mg based molten metal 8, but has not disappeared due to evaporation. When the distance from the bead toe 3 is further increased, the original plating layer 7 exists without melting. In FIG. 3, the thicknesses of the Zn—Al—Mg-based molten metal 8 and the plating layer 7 are exaggerated.

  FIG. 4 schematically shows a cross-sectional structure of a conventional Zn—Al—Mg-based plated steel sheet arc welded structural member obtained by cooling from the state of FIG. In this case, the Zn—Al—Mg based molten metal (reference numeral 8 in FIG. 3) wets and spreads in the “plating layer evaporation region” (reference numeral 9 in FIG. 3) formed once the plating layer disappears during welding, and the base material 1 The entire surface up to the bead toe 3 is covered with the Zn—Al—Mg alloy layer 5. The portion of the Zn—Al—Mg alloy layer 5 formed by solidification of the Zn—Al—Mg molten metal (reference numeral 8 in FIG. 3) is referred to as a molten solidified region 10, and the original plating layer 7 remains and is formed. The portion of the Zn—Al—Mg-based alloy layer 5 is referred to as a plating layer unmelted region 11. In a conventional Zn-Al-Mg-based plated steel sheet arc welded structural member, the bead toe 3 is usually the melt-solidified region 10 as shown in this figure. In this case, since the liquidus temperature of the Zn—Al—Mg-based molten metal 8 is low as described above, the surface portion of the base material 1 that becomes the melted and solidified region 10 after cooling becomes Zn—Al in the cooling process after welding. -The contact time with the Mg-based molten metal is relatively long. Since tensile stress is generated in the portion of the base material 1 near the bead toe due to cooling after welding, the Zn—Al—Mg based molten metal component tends to enter the crystal grain boundary. The said component which penetrate | invaded the grain boundary becomes a factor which causes a molten metal embrittlement crack.

FIG. 5 schematically shows a cross-sectional structure of a Zn—Al—Mg based plated steel sheet arc welded structural member according to the present invention obtained by cooling from the state of FIG. In the present invention, a gas having a greatly reduced CO ₂ concentration or a gas not containing CO ₂ is used as the shielding gas. For this reason, the surface of the base material 1 in the “plating layer evaporation region” (reference numeral 9 in FIG. 3) where the plating layer disappeared during welding is oxidized due to a weak reduction action by the shielding gas, and is quickly covered with a thin oxide film. Conceivable. It is inferred that this oxide film inhibits wetting with the Zn—Al—Mg based molten metal (reference numeral 8 in FIG. 3), thereby suppressing the wetting and spreading of the Zn—Al—Mg based molten metal. As a result, the plating layer evaporation region 9 remains after cooling. That is, the surface of the base material 1 in the vicinity of the bead toe 3 is finished to cool without coming into contact with the Zn—Al—Mg-based molten metal, and the penetration of the molten metal component into the base material 1 at that portion is avoided. Is done. Therefore, excellent molten metal embrittlement cracking resistance is imparted without depending on the steel type of the base material 1. Even in a welding posture in which the height position of the Zn—Al—Mg-based molten metal (reference numeral 8 in FIG. 3) is above the bead toe 3, the above-described Zn—Al—Mg due to the above-described wetting inhibition action. Wetting and spreading of the molten metal is remarkably suppressed.

  The length of the plating layer evaporation region 9 remaining after cooling from the bead toe 3 is referred to as “plating layer evaporation region length” in this specification, and is indicated by the symbol L in FIG. Most of the molten metal embrittlement cracks which are a problem in the Zn—Al—Mg plated steel sheet arc welded structural member occur in the vicinity of the bead toe 3. As a result of various studies, if the plating layer evaporation region length is 0.3 mm or more, the molten metal embrittlement cracking resistance is greatly improved, and if it is 0.4 mm or more, it is more preferable. If this plating layer evaporation region length becomes too long, there will be a problem of deterioration of corrosion resistance due to the absence of the plating layer, but according to the study by the inventors, if the plating layer evaporation region length is 2.0 mm or less, It was found that the sacrificial anticorrosive action by the Zn—Al—Mg based plating layer was sufficiently obtained, and the corrosion resistance reduction at this portion was at a level that would not be a problem. By adjusting the shield gas composition as described later, the plating layer evaporation region length can be controlled within the range of 0.3 to 2.0 mm.

[Gas shield arc welding conditions]
In the arc welding according to the present invention, it is important that the CO ₂ concentration of the shielding gas is in the range of 0 to 7% by volume. As described above, CO ₂ mixed in the shielding gas comes into contact with the plasma arc and partly dissociates into CO and O ₂ , and the base metal surface near the weld bead is activated by the reduction action of the CO. In conventional gas shielded arc welding, it is possible to achieve the above reduction effect sufficiently by using a shielding gas mixed with about 20% by volume of CO ₂ and to increase the penetration depth by stabilizing the arc. It is normal. However, in the present invention, by suppressing the reduction action or not using it at all, it is possible to prevent the surface of the base material where the plating layer in the vicinity of the welded portion has evaporated and lost from being excessively activated, and the surface of the surrounding base material Zn—Al—Mg based molten metal present in the bead is prevented from spreading to the bead toes. As a result of detailed examination, when the CO ₂ concentration is set to 7% or less, the effect of suppressing the wetting and spreading is exhibited, and the above-mentioned plating layer evaporation region length can be controlled within the range of 0.3 to 2.0 mm. Become. It is more effective to set the CO ₂ concentration to less than 5.0%. The base gas of the shielding gas can be Ar gas as in the conventional case. He gas or Ar + He mixed gas may be used. The purity of those base gases may be set to the same level as before.

  For other welding conditions, for example, the shield gas flow rate is adjusted to 10 to 30 L / min, the welding current is set to 90 to 350 A, the arc voltage is set to 10 to 35 V, and the welding speed is adjusted within the range of 0.2 to 1.5 m / min. Good. Conventional welding devices can be used.

An experimental example in which the relationship between the CO ₂ concentration in the Ar gas and the plating layer evaporation region length is examined is introduced.
The molten Zn—Al—Mg based plated steel sheet shown in Table 1 was placed horizontally, and a weld bead was formed on the steel sheet surface by an arc generated from a horizontally moving welding torch (bead on plate). The welding conditions are listed in Table 1. The cross section perpendicular to the bead direction including the weld bead and the base material in the vicinity thereof is mirror-polished and etched with a nitric acid solution with a nitric acid concentration of 0.2% by volume. By observing the vicinity, the plating layer evaporation region length indicated by the symbol L in FIG. 5 was measured.

The result is shown in FIG. As can be seen from FIG. 6, when the CO ₂ concentration in the shielding gas is 7% by volume or less, the phenomenon of cooling while leaving the plating layer evaporation region clearly appears, and the plating layer evaporation region length of 0.3 mm or more is shown. Secured. The three plots located near the CO ₂ concentration of 5% by volume are examples of the CO ₂ concentration of 4.8% by volume. Thus, by setting the CO ₂ concentration to less than 5.0% by volume, the plating layer evaporation region length Can be made 0.8 mm or more, and extremely good resistance to molten metal embrittlement cracking can be realized.

[Fused Zn-Al-Mg plated steel sheet member]
In the present invention, a molten Zn—Al—Mg based plated steel sheet member is applied to at least one of both members joined by arc welding.
Various steel types can be adopted as the plating original plate of the molten Zn—Al—Mg-based plated steel plate member depending on the application. High tensile steel plates can also be used. The plate thickness of the plating original plate can be set to 1.0 to 6.0 mm.

  Specifically, the composition of the molten Zn—Al—Mg-based plating layer is, by mass, Al: 1.0-22.0%, preferably 4.0-22.0%, Mg: 0.05-10. 0%, Ti: 0 to 0.10%, B: 0 to 0.05%, Si: 0 to 2.0%, Fe: 0 to 2.5%, balance Zn and inevitable impurities be able to. The plating layer composition substantially reflects the hot-dip plating bath composition. Although the method of hot dipping is not particularly limited, it is generally advantageous in terms of cost to use an in-line annealing type hot dipping equipment. Hereinafter, the component elements of the plating layer will be described. “%” Of the plating layer component element means “mass%” unless otherwise specified.

  Al is effective in improving the corrosion resistance of the plated steel sheet, and suppresses the generation of Mg oxide dross in the plating bath. In order to fully exhibit these actions, it is necessary to secure an Al content of 1.0% or more, and it is more preferable to secure an Al content of 4.0% or more. On the other hand, when the Al content increases, a brittle Fe—Al alloy layer easily grows on the base of the plating layer, and excessive growth of the Fe—Al alloy layer causes a decrease in plating adhesion. As a result of various studies, the Al content is more preferably 22.0% or less, and may be controlled to 15.0% or less, or even 10.0% or less.

  Mg exhibits the effect | action which produces | generates a uniform corrosion product on the surface of a plating layer, and raises the corrosion resistance of a plated steel plate remarkably. The Mg content is more preferably 0.05% or more, and more preferably 1.0% or more. On the other hand, if the Mg content in the plating bath increases, Mg oxide-based dross is likely to occur, which causes a reduction in the quality of the plating layer. The Mg content is desirably in the range of 10.0% or less.

  When Ti and B are contained in the hot dipping bath, there are advantages such as an increase in the degree of freedom of manufacturing conditions during hot dipping. For this reason, 1 type or 2 types of Ti and B can be added as needed. It is more effective to add 0.0005% or more in the case of Ti and 0.0001% or more in the case of B. However, when the content of Ti or B in the plating layer becomes excessive, it causes a poor appearance of the plating layer surface due to the formation of precipitates. When these elements are added, it is desirable that Ti: 0.10% or less and B: 0.05% or less.

  When Si is contained in the hot dipping bath, excessive growth of the Fe—Al alloy layer formed at the interface between the plating original plate surface and the plating layer is suppressed, and the workability of the hot-dip Zn—Al—Mg plated steel sheet is improved. This is advantageous. Therefore, Si can be contained as necessary. In that case, it is more effective to set the Si content to 0.005% or more. However, since excessive Si content causes an increase in the dross amount in the hot dipping bath, the Si content is preferably 2.0% or less.

  In the hot dipping bath, Fe is likely to be mixed because the steel sheet is immersed and passed. The Fe content in the Zn—Al—Mg plating layer is preferably 2.5% or less.

When the coating amount of the molten Zn—Al—Mg-based steel sheet member is small, it is disadvantageous for maintaining the corrosion resistance and sacrificial anticorrosive action of the plated surface for a long time. As a result of various studies, when the “plating layer evaporation region” generated in the vicinity of the bead toe according to the present invention is left, the Zn—Al—Mg based plating adhesion amount per side is preferably 20 g / m ² or more. It is effective. On the other hand, when the plating adhesion amount increases, blow holes are likely to occur during welding. When blow holes occur, the welding strength decreases. For this reason, it is desirable that the amount of plating deposited on one side be 250 g / m ² or less.

[Parts to be welded]
The mating member to be joined by arc welding to the above molten Zn—Al—Mg based plated steel sheet member may be the same molten Zn—Al—Mg based plated steel sheet member as described above, or other steel materials. It doesn't matter.

A cold-rolled steel strip having a thickness of 3.2 mm and a width of 1000 mm having the composition shown in Table 2 is passed through a hot dipping line to produce hot-dip Zn—Al—Mg-based plated steel plates having various plating layer compositions, Gas shield arc welding was performed by the following test method, and the influence of the shielding gas composition on the resistance to molten metal embrittlement cracking was investigated. The plating layer composition, the plating adhesion amount, and the shielding gas composition are shown in Table 4 below. The shielding gas applied to the examples of the present invention has one or more compositions of CO ₂ : 0 to 7% by volume and the balance: Ar and He.

[Test method for molten metal embrittlement crack resistance]
As shown in FIG. 7, a boss (projection) 15 of a steel bar having a diameter of 20 mm and a length of 25 mm is vertically set up at the center of a 100 mm × 75 mm test piece 14 (molten Zn—Al—Mg-based plated steel plate member). The test piece 14 and the boss 15 were joined by gas shield arc welding under the welding conditions shown in FIG. Specifically, the boss 15 is rotated once around the boss 15 clockwise from the welding start point S, and after the welding start point S is passed, welding is further performed by overlapping the beads, and an overlapping portion 17 of the weld bead 16 is generated. Welding was performed up to a later welding end point E. During welding, the test piece 14 was held on a flat plate. This test was conducted in a situation where welding cracks are likely to occur experimentally.

  After welding, the cut surface 20 passing through the central axis of the boss 15 and passing through the bead overlap portion 17 is observed on the test piece 14 by observing the test piece 14 near the bead overlap portion 17 with a scanning electron microscope. The deepest crack depth (maximum crack depth) was measured. This crack is judged to be a “molten metal embrittlement crack”. The results are shown in Table 4.

As shown in Table 4, molten metal embrittlement cracking was observed in the comparative example in which the CO ₂ concentration in the shielding gas was 9% by volume or more. In any of these, the plating layer evaporation region length L (see FIG. 3) in the test piece 14 is less than 0.3 mm, and the deepest molten metal embrittlement crack has a distance from the toe portion of most samples of about 0.3 mm. It occurred at a site within 3 mm. On the other hand, no molten metal embrittlement cracking was observed in the examples of the present invention in which the CO ₂ concentration in the shielding gas was 7% or less. The plating layer evaporation region length L in the examples of the present invention is 0.3 mm or more, and in particular, the plating layer evaporation region length L in the example in which the CO ₂ concentration is less than 5% is 0.6 mm or more. It was.

DESCRIPTION OF SYMBOLS 1, 1 'base material 2 Weld bead 3 Bead toe part 5 Zn-Al-Mg type alloy layer 6 Fe-Al type alloy layer 7 Plating layer 8 Zn-Al-Mg type molten metal 9 Plating layer evaporation area 10 Melt solidification Area 11 Plating layer unmelted area 14 Test piece 15 Boss 16 Weld bead 17 Bead overlap part 31 Welding torch 32 Welding wire 33 Electrode 34 Shielding gas 35 Arc

Claims (4)

When manufacturing a welded structural member by joining steel materials by gas shielded arc welding (except when a flux-cored wire is used), at least one member to be joined is a molten Zn—Al—Mg-based plated steel sheet. and member, CO _2: 0 to 7% by volume, remainder: Ar, using a shielding gas having a composition is one or more of He, Zn-Al-Mg-based plated steel sheet arcs having excellent liquid metal embrittlement cracking resistance Manufacturing method for welded structural members.   The molten Zn—Al—Mg-based plated steel sheet is, by mass, Al: 1.0 to 22.0%, Mg: 0.05 to 10.0%, Ti: 0 to 0.10%, and B: 0. 2. The molten metal embrittlement resistance according to claim 1, comprising a plating layer comprising 0.05%, Si: 0 to 2.0%, Fe: 0 to 2.5%, the balance Zn and inevitable impurities. A method for producing a Zn-Al-Mg-based plated steel sheet arc welded structural member having excellent crackability. 3. The Zn—Al—Mg system having excellent resistance to molten metal embrittlement cracking according to claim 1, wherein the molten Zn—Al—Mg based plated steel sheet has a plating adhesion amount of 20 to 250 g / m ² per one side. Manufacturing method of plated steel arc welded structural members. The shielding gas, CO ₂ concentration is one which is adjusted to less than 0 vol% to 5.0 vol%, excellent in liquid metal embrittlement cracking resistance according to any one of claims 1 to 3 Zn -Method for producing an Al-Mg plated steel sheet arc welded structural member.

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