Welded member of plated steel sheet having excellent weld zone porosity resistance and fatigue properties and method for manufacturing the same

Abstract

Disclosed are a welded member of plated steel sheet excellent in weld zone porosity resistance and fatigue characteristics and a method for manufacturing the same. A welded member of plated steel sheet excellent in weld zone porosity resistance and fatigue characteristics according to one embodiment of the present invention includes a weld metal portion formed by electric arc welding of a first member and a second member overlapped such that the second member partially overlaps the first member, wherein a toe angle (θ) of the weld metal portion is 45° or less, and the first member and the second member are plated steel sheets.

Description

[0001] This application is a divisional application of Chinese patent application filed on June 18, 2018, with application number "201880009797.8" and invention title "Welded Component of Coated Steel Plate with Excellent Porosity Resistance and Fatigue Characteristics in Welded Zone and its Manufacturing Method Thereof". The original application was the Chinese national phase application of international application PCT / KR2018 / 006856. Technical Field

[0002] This invention relates to welded components of galvanized steel sheets and methods for manufacturing the same, and more specifically to welded components of galvanized steel sheets with excellent porosity resistance and fatigue properties in the weld zone and methods for manufacturing the same. Background Technology

[0003] In the automotive industry, research on weight reduction technologies for vehicle bodies and components has become a major issue in fuel efficiency control strategies aimed at combating environmental problems such as global warming. Chassis components, which are crucial to vehicle performance, also follow this trend, requiring the application of high-strength steel to reduce weight. To achieve weight reduction in components, the strength of the materials must be increased, and ensuring the durability of components made of high-strength steel under repeated fatigue loads is a critical factor.

[0004] In arc welding, primarily used to ensure the strength of assemblies for automotive chassis components, lap welding is performed between components via welding wire, thus the formation of welded joint geometry is unavoidable. This joint acts as a recurring fatigue stress concentration point (notch effect) and becomes the starting point for fracture, thereby reducing the durability of the component and negating the advantages of using high-strength steel.

[0005] As mentioned above, in order to improve the fatigue characteristics of the weld, it is important to reduce the angle of the weld joint end (the main stress concentration area), i.e., the toe angle. At the same time, controlling the material and stress at the toe is also important.

[0006] Furthermore, as mentioned above, due to the increasing demand for rust-resistant properties to prevent penetration corrosion caused by material thinning due to the high strength and light weight of components, there is a growing tendency to use galvanized steel materials such as those in prior art 1. However, galvanized steel materials are sensitive to the occurrence of porosity defects (e.g., pits or porosity) during arc welding, and there are problems with reduced weld strength and fatigue properties.

[0007] On the other hand, although the application of Zn-Mg-Al high corrosion-resistant alloy steel with much higher corrosion resistance than existing hot-dip galvanized steel sheets has been proposed, the melting point and evaporation point of ternary alloy coatings are lower than those of conventional zinc coatings, and the generation of coating vapor is more sensitive. Therefore, it is necessary to develop technologies to suppress the occurrence of porosity defects in welds.

[0008] Although the prior art 1 proposes to set the gap of the lap joint in the range of 0.2 mm to 1.5 mm to suppress the generation of hole defects in the arc welded part of galvanized steel sheet, there is a limitation that the welding characteristics of the joint structure without gap cannot be guaranteed when applying actual parts.

[0009] Furthermore, in prior art 2, to suppress the formation of pore defects in the arc weld of galvanized steel sheets, it is proposed to use a triple-mixed gas of CO2 and O2 mixed with Ar and a low-viscosity solid welding wire, which limits the content of Si and Mn. Additionally, it is proposed that the arc position at the tip of the weld lap joint be 1 mm. However, limitations on the shielding gas and welding materials are unavoidable, and the arc position must be kept constant when applying it to actual components.

[0010] (Patent Document 0001) Japanese Patent Publication No. 2016-101593

[0011] (Patent Document 0002) Japanese Patent Publication No. 2015-167981 Summary of the Invention

[0012] Technical issues

[0013] One embodiment of the present invention seeks to provide welded components of coated steel sheets having excellent resistance to porosity and fatigue properties in the weld zone.

[0014] Furthermore, embodiments of the present invention seek to provide a method for manufacturing welded components of coated steel sheets having excellent resistance to porosity and fatigue in the weld zone.

[0015] Technical solution

[0016] According to one embodiment of the present invention, a welded component of a clad steel sheet having excellent resistance to porosity and fatigue in the weld zone comprises: a weld metal portion formed by arc welding of the first component by overlapping a first component and a second component to form a second component portion, wherein the toe angle (θ) of the weld metal portion is 45° or less, and the first component and the second component are clad steel sheets.

[0017] Furthermore, according to one embodiment of the present invention, the coated steel sheet can be a Zn-Mg-Al alloy coated hot-rolled steel sheet or a galvanized hot-rolled steel sheet.

[0018] Furthermore, according to one embodiment of the present invention, the tensile strength of the hot-rolled steel sheet can be 590 MPa or higher, and the thickness can be 6 mm or less.

[0019] Furthermore, according to one embodiment of the present invention, the hot-rolled steel sheet can be 590FB steel.

[0020] Furthermore, according to one embodiment of the present invention, the hole area ratio of the weld metal portion can be less than 0.5%.

[0021] Furthermore, according to one embodiment of the invention, the fatigue strength of the weld metal portion can be 250 MPa or greater, and the fatigue life under a cyclic fatigue load of 10 kN (minimum / maximum load ratio, R = 0.1) can be 2,000,000 or more cycles.

[0022] A method for manufacturing a welded component of a clad steel sheet having excellent weld zone porosity and fatigue properties according to an embodiment of the present invention includes: forming a weld metal portion by overlapping a first component and a second component to form a second component partially overlapping the first component and performing arc welding, wherein the first component and the second component are clad steel sheets; applying a welding current to a solid welding wire to generate an arc, wherein the welding current is a pulsed current that repeats with a first peak and a second peak with a current value less than the first peak as a pulse period, and the frequency of the molten weld metal stirring wave defined by the following formula (1) is 20 Hz to 30 Hz.

[0023] 1 / (T H + T L Formula (1)

[0024] Here, T H The period of the first peak, and T L This is the period of the second peak.

[0025] Furthermore, according to one embodiment of the invention, solid welding wire can be fed into a protective gas consisting of Ar gas containing 10% to 30% CO2 gas.

[0026] Furthermore, according to one embodiment of the invention, the welding current can be in the range of 200 A to 300 A.

[0027] Furthermore, according to one embodiment of the present invention, during arc welding, the diameter of the solid welding wire can be from 1.0 mm to 1.2 mm, the torch angle can be from 30° to 45°, the push angle can be from 0° to 25°, and the welding speed can be from 0.6 m / min to 1.0 m / min.

[0028] Furthermore, according to one embodiment of the present invention, the first component and the second component may be hot-rolled steel sheet coated with Zn-Mg-Al alloy or hot-rolled steel sheet coated with zinc.

[0029] Furthermore, according to one embodiment of the present invention, the tensile strength of the hot-rolled steel sheet can be 590 MPa or higher, and the thickness can be 6 mm or less.

[0030] Beneficial effects

[0031] In the production of welded components of coated steel sheets with excellent resistance to porosity and fatigue in the weld zone according to one embodiment of the present invention, porosity defects in the weld metal can be effectively reduced by optimizing the wave frequency of the welding current. Fatigue stress concentration on the weld toe can be reduced by controlling the toe angle of the weld metal. Therefore, highly corrosion-resistant coated steel sheets can be used to ensure high strength of components (e.g., chassis components of automobiles) and rust-resistant properties due to the thinning of the components. Thus, welded components of coated steel sheets with excellent resistance to porosity and fatigue in the weld zone can be obtained. Attached Figure Description

[0032] Figure 1 This is a photograph of a cross-section of a welded member of a plated steel sheet having excellent resistance to porosity and fatigue in the weld zone, according to an embodiment of the present invention.

[0033] Figure 2 This is a photograph showing the appearance of a weld according to one embodiment of the present invention.

[0034] Figure 3 This is an X-ray photograph showing the appearance of a weld according to one embodiment of the present invention.

[0035] Figure 4 This is a photograph showing the tensile fracture test results of a welded component of a plated steel sheet according to an example of the present invention.

[0036] Figure 5 This is a schematic diagram illustrating the weld metal portion of a welded component of a plated steel sheet according to an embodiment of the present invention.

[0037] Figure 6 This is a graph illustrating the molten metal agitation wave frequency during arc welding of a welded component of a coated steel sheet according to an embodiment of the present invention.

[0038] Best practice

[0039] A welded component of a clad steel sheet with excellent resistance to porosity and fatigue in the weld zone includes: a weld metal portion formed by arc welding of a first component and a second component overlapping the second component portion, wherein the toe angle (θ) of the weld metal portion is 45° or less, and the first component and the second component are clad steel sheets. Detailed Implementation

[0040] In the following, embodiments of the invention will be described in detail with reference to the accompanying drawings. The following embodiments are presented to fully convey the spirit of the invention to those skilled in the art. The invention is not limited to the embodiments presented herein, but may be implemented in other forms. For clarity, descriptions of parts irrelevant to the description have been omitted from the drawings, and the dimensions of components may be expressed in a slightly exaggerated manner for ease of understanding.

[0041] Figure 1 This is a photograph of a cross-section of a welded member of a plated steel sheet having excellent resistance to porosity and fatigue in the weld zone, according to an embodiment of the present invention. Figure 2 This is a photograph showing the appearance of a weld according to one embodiment of the present invention. Figure 3 This is an X-ray photograph showing the appearance of a weld according to one embodiment of the present invention. Figure 4 This is a photograph showing the tensile fracture test results of a welded component of a plated steel sheet according to an example of the present invention. Figure 5 This is a schematic diagram illustrating the weld metal portion of a welded component of a plated steel sheet according to an embodiment of the present invention.

[0042] Reference Figures 1 to 5 According to one embodiment of the present invention, a welded component of a plated steel sheet having excellent resistance to porosity and fatigue in the weld zone includes: a weld metal portion formed by arc welding of a first component and a second component overlapping the second component portion to form a second component portion overlapping the first component.

[0043] At this point, the toe angle (θ) of the weld metal is 45° or less.

[0044] Methods to improve the fatigue characteristics of welded components can be broadly categorized into methods that utilize residual stress and methods that control the shape of the weld bead.

[0045] In the context of this invention, one objective is to improve the fatigue characteristics of the welded component by controlling the weld shape. For this purpose, the toe angle of the weld metal portion is set to 45° or less (excluding 0°), preferably 35° or less (excluding 0°), and more preferably 30° or less (excluding 0°).

[0046] Here, the toe angle refers to the angle formed by the tangent of the bend in the weld closest to the boundary line between the first and second components and the weld toe of the weld metal portion, with the weld toe serving as a reference point. In this case, the contact point between the boundary line between the first and second components and the weld metal portion in a section perpendicular to the weld line is defined as the weld toe.

[0047] By forming a toe angle of 45° or less, stress concentrated on the weld metal can be reduced, and at the same time, the fatigue characteristics of the welded component can be improved.

[0048] By controlling the toe angle of the weld metal portion as described above, the fatigue characteristics of the weld portion can be improved. However, to maximize the effect, it is preferable to appropriately control the penetration depth of the weld metal portion. According to one embodiment of the invention, the penetration depth of the weld metal portion can be controlled to be 20% or more of the thickness of the second member. More preferably, the penetration depth of the weld metal portion can be controlled to be 45% or more of the thickness of the second member. If the penetration depth of the weld metal portion is insufficient, fatigue loading may cause the weld metal portion to fracture from the bead route due to repeated fatigue loading.

[0049] In addition, the first and second components are galvanized steel plates.

[0050] Therefore, by using galvanized steel sheets instead of ordinary hot-rolled steel sheets, rust-proof properties can be ensured to prevent penetrating corrosion caused by material thinning due to the high strength and light weight of the components.

[0051] For example, the clad steel sheet can be a hot-rolled steel sheet coated with a Zn-Mg-Al alloy or a galvanized hot-rolled steel sheet. More preferably, the clad steel sheet can be a hot-rolled steel sheet coated with a Zn-Mg-Al alloy, which is more corrosion-resistant than galvanized hot-rolled steel sheet.

[0052] For example, the tensile strength of the hot-rolled steel sheet can be 590 MPa or higher and the thickness can be 6 mm or less, and the hot-rolled steel sheet can be 590FB steel with a microstructure containing ferrite and bainite.

[0053] For example, the area ratio of holes formed in the weld metal portion can be less than 0.5%.

[0054] When welding galvanized steel sheets using conventional arc welding methods, numerous porosity defects, such as pits or pores, are generated due to the production of coating vapor when the coating comes into contact with the welding arc, leading to reduced strength and fatigue characteristics of the weld. Furthermore, in the case of Zn-Mg-Al type high-corrosion-resistant alloy coatings, which offer superior corrosion resistance compared to conventional galvanized steel sheets, the melting and evaporation points of the ternary alloy coatings are significantly lower. Therefore, the problem is that a greater amount of coating vapor is generated, and the incidence of porosity defects is higher.

[0055] However, the manufacturing method according to one embodiment of the invention, which includes arc welding, minimizes these problems by using not only existing galvanized steel sheets but also steel sheets coated with a Zn-Mg-Al high corrosion-resistant alloy. In any case, the hole area ratio of the weld metal portion can be limited to less than 0.5%, preferably 0%.

[0056] For example, the fatigue strength of the weld metal is 250 MPa or higher, and a fatigue life of 2,000,000 or more cycles can be ensured under a cyclic fatigue load of 10 kN (minimum / maximum load ratio, R = 0.1). It can be seen that the component has excellent fatigue characteristics. In this case, the fatigue strength (or fatigue limit) is defined as the value obtained by dividing the maximum fatigue load value when the fatigue life becomes 2,000,000 or more cycles by the cross-sectional area of ​​the component.

[0057] A method for manufacturing a welded component of a galvanized steel sheet having excellent resistance to porosity and fatigue in the weld zone includes the step of forming a weld metal portion by overlapping a first component and a second component to partially overlap the first component and performing arc welding.

[0058] First, after preparing the first and second components, a welding line is formed by stacking the second component on top of the first component so that at least a portion of them overlap. Here, the welding line refers to the end of the second component in the area where the first and second components overlap.

[0059] The overlap width of the welded joint can be from about 5 mm to 50 mm, but is not limited to this.

[0060] At this point, while providing a protective gas, arc welding is performed along the formed weld line, and during arc welding, welding current is supplied to the solid welding wire to generate an arc for welding.

[0061] For example, solid welding wire can be fed into a shielding gas consisting of Ar gas containing 10% to 30% CO2 gas. More preferably, the shielding gas can be Ar gas containing 10% to 20% CO2 gas.

[0062] That is, the protective gas is Ar gas and contains 10% to 30% CO2 gas. If the CO2 gas content is less than 10%, the effect of arc heat pinch force caused by arc contraction is reduced, and the effect of venting coating vapors is reduced. If the CO2 gas content is greater than 30%, the effect of arc heat pinch force caused by arc expansion is too large, and the effect of venting coating vapors is reduced.

[0063] When the first and second components to be welded are coated steel sheets, for example, in the case of galvanized steel sheets, the arc heat during arc welding causes the galvanized layer with a low boiling point to float as zinc gas on top of the molten portion. Most of the zinc is released, but a portion remains in the molten portion, forming pits as small depressions when the zinc gas near the substrate surface solidifies. For example, by using Ar gas containing CO2 as a shielding gas, the weld below the solid wire can be thoroughly welded in gas-shielded arc welding by increasing the arc force generated between the solid wire and the substrate. Therefore, the removal of zinc gas generated in the lower part of the molten metal can be promoted, and the penetration depth of the weld metal portion can be further increased during gas-shielded arc welding. Ultimately, the occurrence of depression defects can be suppressed and the fatigue characteristics of the weld portion can be improved.

[0064] Solid welding wire can be used as a welding material. For example, ER70S-3 (KC-25M) 1.2 solid welding wire can be used, but it is not particularly limited to this.

[0065] For example, the welding current is a pulsed current that repeats with a pulse cycle consisting of a first peak and a second peak with a current value less than the first peak.

[0066] Welding is performed by repeatedly supplying pulsed current at a welding molten metal stirring wave frequency of 20 Hz to 30 Hz, defined by the following formula (1).

[0067] 1 / (T H + T L Formula (1)

[0068] Here, T H The period of the first peak, and T L This is the period of the second peak.

[0069] Figure 6 This is a diagram illustrating the frequency of molten metal agitation waves during arc welding of a welded component of a plated steel sheet according to an embodiment of the present invention.

[0070] The frequency of the agitation wave of the molten welding metal is limited to 1 / (T) H + T L ),like Figure 6 As shown. Therefore, a pulsed current is repeatedly supplied in the range of 20 Hz to 30 Hz. If this frequency range is too low or too high, the effect of venting coating vapor may be reduced, which may make it difficult to reduce pore defects.

[0071] For example, the welding current can be in the range of 200 A to 300 A.

[0072] More preferably, the lower limit of the welding current can be 225 A or higher, and the upper limit can be 270 A or lower. If the current is too low, the effect of venting coating vapors will decrease due to the reduction in arc power. On the other hand, if the current is too high, the weld metal becomes unstable, and the incidence of hole defects increases.

[0073] For example, in arc welding, the diameter of the solid welding wire can be from 1.0 mm to 1.2 mm, the torch angle can be from 30° to 45°, the push angle can be from 0° to 25°, and the welding speed can be from 0.6 m / min to 1.0 m / min.

[0074] In embodiments of the present invention, although the gap of the welded joint is 0 mm, it is not limited thereto.

[0075] Furthermore, the first and second components can be Zn-Mg-Al alloy-coated hot-rolled steel sheets or galvanized hot-rolled steel sheets. The tensile strength of the hot-rolled steel sheet can be 590 MPa or higher, and the thickness can be 6 mm or less. The detailed description of the first and second components is the same as described above and will not be repeated.

[0076] The invention will be described in more detail below through examples.

[0077] Invention Examples 1 to 4 and Comparative Examples 1 to 6

[0078] Two pieces were coated with Zn-Mg-Al with a coating weight of 90 g / m. 2 A 2.2 mm thick 590FB plate was placed on both sides of the steel plate, overlapping each other by 20 mm. The connecting parts were then welded by arc welding according to the conditions shown in Table 1 below.

[0079] [Table 1]

[0080]

[0081] The presence of pits and the ratio of hole area were measured by observing the weld metal portion of the welded component, as shown in Table 2 below.

[0082] [Table 2]

[0083]

[0084] Figure 5 This is a schematic diagram illustrating the weld metal portion of a welded component of a plated steel sheet according to an embodiment of the present invention.

[0085] exist Figure 5 In the figure, the width of the weld metal portion (i.e., the leg length) is L, the thickness of the second member is h1, the distance from the straight line from the upper surface edge of the second member to the toe of the first member to the contact point between the first and second members and the weld metal portion is d, the distance to the highest surface of the weld metal portion is r, the penetration depth is p, and the toe angle is θ. Table 3 shows the observed dimensions of the weld metal portion according to an embodiment of the present invention.

[0086] [Table 3]

[0087]

[0088] Referring to the above, according to one embodiment of the present invention, the toe angle of the weld metal portion of the welded component can be maintained at 45° or less, and no pits or holes are generated in the weld metal portion. Therefore, the porosity of the welded component of the galvanized steel sheet can be improved. The strength of the weld metal portion can be ensured at 250 MPa or higher, and the application range of high-strength galvanized hot-rolled sheet steel for making components such as automotive chassis components thinner and lighter can be increased.

[0089] Industrial applicability

[0090] The welded components of plated steel sheets with excellent resistance to porosity and fatigue in the weld zone, as described in embodiments of the present invention, and the method for manufacturing the same, can be applied to components such as automotive chassis components.

[0091] This application also relates to the following aspects:

[0092] 1. A welded component of a galvanized steel sheet exhibiting excellent resistance to porosity and fatigue in the weld zone, comprising:

[0093] The weld metal portion is formed by arc welding of the first component and the second component, where the second component partially overlaps the first component.

[0094] The toe angle (θ) of the weld metal portion is 45° or less, and the first and second components are plated steel sheets.

[0095] 2. The welded component of the clad steel sheet according to aspect 1, wherein the clad steel sheet is a Zn-Mg-Al alloy hot-rolled steel sheet or a galvanized hot-rolled steel sheet.

[0096] 3. The welded component of the galvanized steel sheet according to aspect 2, wherein the hot-rolled steel sheet has a tensile strength of 590 MPa or higher and a thickness of 6 mm or less.

[0097] 4. The welded component of the galvanized steel sheet according to aspect 3, wherein the hot-rolled steel sheet is 590FB steel.

[0098] 5. The welded component of the galvanized steel sheet according to aspect 1, wherein the hole area ratio of the weld metal portion is less than 0.5%.

[0099] 6. The welded component of the clad steel sheet according to aspect 1, wherein the fatigue strength of the weld metal portion is 250 MPa or greater, and the fatigue life is 2,000,000 or more cycles under a cyclic fatigue load of 10 kN (minimum / maximum load ratio, R = 0.1).

[0100] 7. A method for manufacturing welded components from coated steel sheets having excellent resistance to porosity and fatigue in the weld zone, comprising:

[0101] A weld metal portion is formed by overlapping a first component and a second component to form a portion of the second component overlapping the first component and then performing arc welding, wherein the first component and the second component are clad steel plates;

[0102] A welding current is applied to a solid welding wire to generate an electric arc.

[0103] The welding current is a pulsed current that repeats with a pulse cycle consisting of a first peak and a second peak with a current value less than the first peak, and...

[0104] The frequency of the agitation wave of the molten welding metal, as defined by equation (1), is 20 Hz to 30 Hz.

[0105] 1 / (T H + T L Formula (1)

[0106] Here, T H The period of the first peak, and T L This represents the period of the second peak.

[0107] 8. The method according to aspect 7, wherein the solid welding wire is fed into a protective gas consisting of Ar gas containing 10% to 30% CO2 gas.

[0108] 9. The method according to aspect 7, wherein the welding current is in the range of 200 A to 300 A.

[0109] 10. The method according to aspect 7, wherein the diameter of the solid welding wire is 1.0 mm to 1.2 mm, the welding torch angle is 30° to 45°, the push angle is 0° to 25°, and the welding speed is 0.6 m / min to 1.0 m / min.

[0110] 11. The method according to aspect 7, wherein the first component and the second component are Zn-Mg-Al alloy coated hot-rolled steel sheets or galvanized hot-rolled steel sheets.

[0111] 12. The method according to aspect 11, wherein the hot-rolled steel sheet has a tensile strength of 590 MPa or higher and a thickness of 6 mm or less.

Claims

1. A welded component made of plated steel sheet, comprising: The weld metal portion is formed by arc welding of the first component and the second component, where the second component partially overlaps the first component. The toe angle (θ) of the weld metal portion is 45° or less, and the first and second components are plated steel sheets. The penetration depth of the weld metal portion is 20% or more of the thickness of the second component.

2. The welded component of the clad steel sheet according to claim 1, wherein the clad steel sheet is a Zn-Mg-Al alloy hot-rolled steel sheet or a galvanized hot-rolled steel sheet.

3. The welded component of the galvanized steel sheet according to claim 2, wherein the hot-rolled steel sheet has a tensile strength of 590 MPa or higher and a thickness of 6 mm or less.

4. The welded component of the galvanized steel sheet according to claim 3, wherein the hot-rolled steel sheet is 590FB steel.

5. The welded component of the plated steel sheet according to claim 1, wherein the hole area ratio of the weld metal portion is less than 0.5%.

6. The welded component of the clad steel sheet according to claim 1, wherein the fatigue strength of the weld metal portion is 250 MPa or greater, and the fatigue life under a cyclic fatigue load of 10 kN (minimum / maximum load ratio, R = 0.1) is 2,000,000 or more cycles.

7. A method for manufacturing a welded component made of galvanized steel sheet, comprising: A weld metal portion is formed by overlapping a first component and a second component, with the second component partially overlapping the first component, and then performing arc welding. The first component and the second component are galvanized steel plates; A welding current is applied to a solid welding wire to generate an electric arc. The welding current is a pulsed current that repeats with a pulse cycle consisting of a first peak and a second peak with a current value less than the first peak, and... The frequency of the agitation wave of the molten welding metal, as defined by equation (1), is 20 Hz to 30 Hz. 1 / (T H + T L Formula (1) Here, T H The period of the first peak, and T L This represents the period of the second peak.

8. The method of claim 7, wherein the solid welding wire is fed into a protective gas consisting of Ar gas containing 10% to 30% CO2 gas.

9. The method according to claim 7, wherein the welding current is in the range of 200 A to 300 A.

10. The method according to claim 7, wherein the diameter of the solid welding wire is 1.0 mm to 1.2 mm, the welding torch angle is 30° to 45°, the push angle is 0° to 25°, and the welding speed is 0.6 m / min to 1.0 m / min.

11. The method according to claim 7, wherein the first component and the second component are Zn-Mg-Al alloy coated hot-rolled steel sheets or galvanized hot-rolled steel sheets.

12. The method of claim 11, wherein the hot-rolled steel sheet has a tensile strength of 590 MPa or higher and a thickness of 6 mm or less.

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