High-strength hot-dip galvanized steel sheet excellent in plating adhesion and weldability and method for producing the same

Abstract

One embodiment of the present invention provides a high-strength hot-dip galvanized steel sheet having excellent coating adhesion and weldability, the hot-dip galvanized steel sheet having a base steel sheet and a hot-dip galvanized layer formed on one or both sides of the base steel sheet, the base steel sheet containing, by weight, 0.1-0.3% carbon (C), 0.1-2.0% silicon (Si), 0.1-1.5% aluminum (Al), 1.5-3.0% manganese (Mn), the balance being Fe and unavoidable impurities, the total of the Si and Al satisfying 1.2-3.5%, the ratio of the Al and Si (Al / Si) satisfying 0.5-2.0, the base steel sheet containing an internal oxide layer having a thickness of 1-5 μm immediately below the surface of the base steel sheet, and a decarburization rate of 50% or more in a region from immediately below the surface to 50 μm below the surface of the base steel sheet, and a manufacturing method thereof.

Description

Technical Field

[0001] The present invention relates to a high-strength hot-dip galvanized steel sheet excellent in plating adhesion and weldability and a method for manufacturing the same.

Background Art

[0002] Recently, due to emerging environmental regulations, the demand for ultra-high-strength steel sheets has been rapidly increasing as a solution to meet the strict fuel consumption regulations and enhanced collision stability regulations for automobiles. Also, while fuel efficiency improvement is required to achieve the national carbon emission reduction targets, the weight of automobiles has been continuously increasing due to performance improvement and the addition of various convenience devices. To solve such problems, the demand for ultra-high-strength steel sheets has also been continuously increasing. Therefore, steelmakers are focusing on the development of high-strength steel sheets such as Dual Phase (DP) steel, Transformation Induced Plasticity (TRIP) steel, and Complex Phase (CP) steel.

[0003] In order to increase the strength of steel sheets for automobiles, it is common to add a large amount of elements such as Si, Mn, and Al to the steel. However, steel sheets containing these elements may have inferior plating properties and cause plating peeling when immersed in a hot-dip galvanizing bath because the above elements generate oxides on the surface of the steel sheet during the annealing heat treatment process. Also, in the subsequent spot welding process, there is a possibility of causing Liquid Metal Embrittlement, where the liquid-phase molten metal penetrates through the base metal grain boundaries and induces cracks, thereby deteriorating the spot weldability.

[0004] In order to improve the plating properties of the steel sheets with a large amount of Si, Mn, and Al added as described above, it is necessary to suppress the oxides generated on the surface of the steel sheet. For this purpose, it is necessary to reduce the addition amounts of Si and Al added to the steel. However, in such a case, there is a problem that it is difficult to secure the target material.

[0005] As a typical technique for solving this problem, there is Patent Document 1. Patent Document 1 relates to a technique for suppressing the formation of SiO2 or the like on the surface by preferentially concentrating trace components such as Sb in steel at grain boundaries by adding them.

[0006] However, there is still a demand for the development of a technique that can more reliably prevent the diffusion of alloy elements in steel during the manufacture of steel sheets.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] One aspect of the present invention is to provide a high-strength hot-dip galvanized steel sheet excellent in plating adhesion and weldability and a method for manufacturing the same.

Means for Solving the Problems

[0009] One embodiment of the present invention is a hot-dip galvanized steel sheet having a base steel sheet and a hot-dip galvanized layer formed on one or both surfaces of the base steel sheet, wherein the base steel sheet contains, by weight%, carbon (C): 0.1 to 0.3%, silicon (Si): 0.1 to 2.0%, aluminum (Al): 0.1 to 1.5%, manganese (Mn): 1.5 to 3.0%, and the balance Fe and unavoidable impurities, the total of Si and Al satisfies 1.2 to 3.5%, the ratio of Al to Si (Al / Si) satisfies 0.5 to 2.0, the base steel sheet contains an internal oxide layer having a thickness of 1 to 5 μm immediately below the surface, and the decarburization rate in the region from immediately below the surface of the base steel sheet to 50 μm is 50% or more, and provides a high-strength hot-dip galvanized steel sheet excellent in plating adhesion and weldability.

[0010] Other embodiments of the present invention include, by weight%, carbon (C): 0.1 to 0.3%, silicon (Si): 0.1 to 2.0%, aluminum (Al): 0.1 to 1.5%, manganese (Mn): 1.5 to 3.0%, the balance being Fe and unavoidable impurities, the total of the above Si and Al satisfying 1.2% or more, and the ratio of the above Al and Si (Al / Si) satisfying 0.5 to 2.0, preparing a base steel sheet; heating the base steel sheet in a gas atmosphere having a dew point temperature of 10 to 20°C and containing, by volume%, 3 to 20% hydrogen, the balance being nitrogen and other unavoidable impurities, in a temperature range of 750 to 900°C; and dipping the heated base steel sheet into a molten zinc plating bath at 440 to 460°C to obtain a hot-dip galvanized steel sheet. A method for manufacturing a high-strength hot-dip galvanized steel sheet excellent in plating adhesion and weldability is provided.

Advantages of the Invention

[0011] According to one aspect of the present invention, a high-strength hot-dip galvanized steel sheet excellent in plating adhesion and weldability and a method for manufacturing the same can be provided.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0013] The following describes a high-strength hot-dip galvanized steel sheet excellent in plating adhesion and weldability according to an embodiment of the present invention. The hot-dip galvanized steel sheet of the present invention has a base steel sheet and a hot-dip galvanized layer formed on one or both surfaces of the base steel sheet. First, the alloy composition of the base steel sheet of the present invention will be described. The contents of the alloy compositions described below mean weight% unless otherwise specified.

[0014] Carbon (C): 0.1 - 0.3% The above C is an element that contributes to the stabilization of the austenite structure, and the increase in its content has an advantageous aspect in ensuring the austenite structure. In order to obtain the above effects, the C content is preferably 0.1% or more. However, when it exceeds 0.3%, there may be problems such as the occurrence of slab defects and a decrease in weldability. Therefore, the content of the above C preferably has a range of 0.1 - 0.3%. The lower limit of the C content is more preferably 0.15%. The upper limit of the C content is more preferably 0.25%.

[0015] Silicon (Si): 0.1 - 2.0% Silicon (Si) is an element that suppresses the precipitation of carbides in ferrite, promotes the diffusion of carbon in ferrite into austenite, and contributes to the stabilization of retained austenite. In order to obtain the above-described effects, it is preferable that the above Si is added in an amount of 0.1% or more. However, when its content exceeds 2.0%, not only is the rollability inferior, but oxides are formed on the surface of the steel sheet during the heat treatment process, which may lead to deterioration of the plating property and adhesion. Therefore, the content of the above Si preferably has a range of 0.1 - 2.0%. The lower limit of the Si content is more preferably 0.2%. The upper limit of the Si content is more preferably 1.8%.

[0016] Aluminum (Al): 0.1 - 1.5% Aluminum (Al) is an element that combines with oxygen in steel to perform a deoxidation function, and Al is an element that suppresses the formation of carbides in ferrite like the above Si and contributes to the stabilization of retained austenite. To obtain the above-described effects, it is preferable that the above Al is added in an amount of 0.1% or more. However, when its content exceeds 1.5%, not only is the soundness of the slab inferior, but since it is an element with a strong oxygen affinity, oxides may be formed on the surface of the steel sheet, which may cause inhibition of plating properties and adhesion. Therefore, it is preferable that the content of the above Al has a range of 0.1 to 1.5%. It is more preferable that the lower limit of the above Al content is 0.2%. It is more preferable that the upper limit of the above Al content is 1.4%.

[0017] Manganese (Mn): 1.5 - 3.0% The above Mn is an element that stabilizes the austenite structure together with carbon. When the above Mn content is less than 1.5%, it becomes difficult to ensure the target strength due to the occurrence of ferrite transformation. When it exceeds 3.0%, due to the formation of martensite caused by the delay of phase transformation during the secondary annealing heat treatment process, difficulties occur in ensuring the target ductility. Therefore, it is preferable that the content of the above Mn has a range of 1.5 - 3.0%. It is more preferable that the lower limit of the above Mn content is 1.7%. It is more preferable that the upper limit of the above Mn content is 2.9%.

[0018] In addition to the above-described steel composition, the remainder can contain Fe and inevitable impurities. Inevitable impurities are those that can be inadvertently mixed in during normal steel manufacturing processes, and it is not possible to completely exclude them. A person skilled in the art of normal steel manufacturing can easily understand its meaning. Note that the present invention does not completely exclude the addition of other compositions other than the above-described steel composition.

[0019] On the one hand, as described above, both Si and Al are elements that contribute to the stabilization of retained austenite. In order to effectively achieve this, it is preferable that the total content of Si and Al satisfies the range of 1.2 to 3.5%. When the total content of Si and Al is less than 1.2%, it may be difficult to sufficiently obtain the effect of increasing the elongation rate. On the contrary, when the total content of Si and Al exceeds 3.5%, problems such as poor castability and rollability may occur. The lower limit of the total content of Si and Al is more preferably 1.3%. The upper limit of the total content of Si and Al is more preferably 3.4%.

[0020] Also, the ratio of Al to Si (Al / Si) is preferably 0.5 to 2.0. When the ratio of Al to Si is less than 0.5, peeling of the plating may occur due to the distribution of Si-rich oxides in the form of a layer. On the contrary, when the ratio of Al to Si exceeds 2.0, Al-rich oxides are densely formed on the surface of the steel sheet, suppressing the penetration of external oxygen into the steel sheet, making it difficult to form an internal oxide layer immediately below the surface of the base steel sheet, and the Al-rich oxides formed in the form of a layer on the surface may result in poor plating properties and adhesion. The lower limit of the ratio of Al to Si is more preferably 0.6. The upper limit of the ratio of Al to Si is more preferably 1.9.

[0021] The hot-dip galvanized steel sheet of the present invention preferably contains an internal oxide layer with a thickness of 1 to 5 μm immediately below the surface of the base steel sheet. By forming an internal oxide layer immediately below the surface of the base steel sheet, the present invention prevents Al and Si present in the base steel sheet from diffusing into the surface layer of the steel sheet, and prevents the formation of Al or Si oxides in the above surface layer, thereby achieving the purpose of improving the plating property. However, when the thickness of the above internal oxide layer is less than 1 μm, it may be difficult to sufficiently obtain the above-described effects. On the other hand, when the thickness of the above internal oxide layer exceeds 5 μm, there is a drawback that oxides on the steel sheet surface may be picked up by the roll during the annealing heat treatment process, resulting in surface defects such as dents. Therefore, the thickness of the above internal oxide layer is preferably 1 to 5 μm. The lower limit of the thickness of the above internal oxide layer is more preferably 1.5 μm, and even more preferably 2 μm. The upper limit of the thickness of the above internal oxide layer is more preferably 4.5 μm, even more preferably 4 μm, and most preferably 3.5 μm.

[0022] The above internal oxide layer can contain an oxide composed of an Al, Si composite oxide. Thus, since the oxide is composed of an Al, Si composite oxide, an effect can be obtained in which the form of the oxide forms a discontinuous form of oxide rather than a continuous form such as a layer, thereby improving the plating adhesion.

[0023] The above Al, Si composite oxide can exist either within the crystal grains or at the grain boundaries. At this time, the above Al, Si composite oxide preferably exists discontinuously. Thus, by making the above Al, Si composite oxide exist discontinuously, it can be more advantageous for ensuring plating adhesion than making it exist continuously.

[0024] On the one hand, for the hot-dip galvanized steel sheet of the present invention, it is preferable that the decarburization rate in the region from just below the surface of the base steel sheet to 50 μm is 50% or more. As proposed by the present invention, when the dew point temperature in the heat treatment furnace is high, internal oxides are formed in the surface layer of the steel sheet, and at the same time, C in the steel reacts with the adsorbed oxygen on the surface of the steel sheet to be gasified into CO or CO2 gas, and a C depletion region is formed in the surface layer of the base material. When such a decarburization reaction occurs, the resistance to spot welding LME cracks becomes excellent. However, when the decarburization rate is less than 50%, the decarburization reaction is insufficient, and there is a possibility of inferior LME crack resistance.

[0025] The hot-dip galvanized steel sheet of the present invention provided as described above has a yield strength of 600 MPa or more, a tensile strength of 950 MPa or more, and an elongation of 20% or more, and can ensure excellent mechanical properties. Also, while the area of the hot-dip galvanized layer with respect to the total area of the base steel sheet is 95% or more, the plating adhesion is good, and excellent plating properties can be obtained. Further, the maximum length of the LME crack is 50 μm or less, and excellent LME crack resistance can be obtained.

[0026] Hereinafter, a method for manufacturing a high-strength hot-dip galvanized steel sheet excellent in plating adhesion and weldability according to an embodiment of the present invention will be described.

[0027] First, a base steel sheet satisfying the above-described alloy composition is prepared. In the present invention, the method for preparing the base steel sheet is not particularly limited. However, as a preferable example, the step of preparing the base steel sheet may include the step of reheating the slab at 1000 to 1300 °C, the step of hot finish rolling the reheated slab at 800 to 950 °C to obtain a hot-rolled steel sheet, the step of coiling the hot-rolled steel sheet at 630 to 700 °C, and the step of pickling the coiled hot-rolled steel sheet and then cold rolling it to obtain a cold-rolled steel sheet.

[0028] The slab that satisfies the above-described alloy composition is reheated at 1000 to 1300°C. When the slab reheating temperature is less than 1000°C, there may be a problem that the rolling load significantly increases. When it exceeds 1300°C, there may be a problem that the surface scale becomes excessive. Therefore, the slab reheating temperature preferably has a range of 1000 to 1300°C. The lower limit of the slab reheating temperature is more preferably 1050°C. The upper limit of the slab reheating temperature is more preferably 1250°C.

[0029] Thereafter, the reheated slab is hot finish rolled at 800 to 950°C to obtain a hot rolled steel sheet. When the hot finish rolling temperature is less than 800°C, there is a problem that the rolling load increases and rolling becomes difficult. When it exceeds 950°C, there is a drawback that the roll life is shortened due to an increase in thermal fatigue of the rolling roll. Therefore, the hot finish rolling temperature preferably has a range of 800 to 950°C. The lower limit of the hot finish rolling temperature is more preferably 830°C. The upper limit of the hot finish rolling temperature is more preferably 930°C.

[0030] Thereafter, the hot rolled steel sheet is coiled at 630 to 700°C. When the coiling temperature is less than 630°C, an internal oxide layer is not formed, so the formation of oxides is promoted in the surface layer portion of the steel sheet during the annealing heat treatment process, and there is a possibility of inferior plating properties. When it exceeds 700°C, the depth of the internal oxide layer becomes considerably deep, and oxides are picked up by the roll during the subsequent annealing heat treatment process, which may induce surface defects such as dents. Therefore, the coiling temperature preferably has a range of 630 to 700°C. The lower limit of the coiling temperature is more preferably 650°C. The upper limit of the coiling temperature is more preferably 680°C.

[0031] Thereafter, the coiled hot rolled steel sheet is pickled and then cold rolled to obtain a cold rolled steel sheet. In the present invention, the pickling and cold rolling processes are not particularly limited, and all methods commonly performed in the art can be used.

[0032] For the substrate steel sheet prepared as described above, it is soaked in a gas atmosphere having a dew point temperature of 10 to 20°C and containing 3 to 20% hydrogen, the balance nitrogen and other inevitable impurities by volume, in a temperature range of 750 to 900°C. The soaking as described above means heating to the above temperature range and then holding. When the dew point temperature is less than 10°C, not only is there a limit to effectively suppressing the surface enrichment of Si and Mn in the steel due to insufficient local internal oxidation, but also the decarburization effect is insufficient, so there may be inferior LME crack resistance. On the other hand, when it exceeds 20°C, since it is a dew point region where Fe can be oxidized, there may be peeling of the plating due to Fe oxide. When the fraction of hydrogen in the gas is less than 3% by volume, sufficient reducing ability cannot be ensured, and Fe oxide etc. may remain on the surface of the steel sheet, causing non-plating or peeling of the plating. When it exceeds 20% by volume, there is a drawback that the cost increases due to the large amount of high-cost hydrogen used. When the soaking temperature is less than 750°C, the recrystallization temperature of A3 or higher cannot be ensured, and there may be variations in mechanical properties due to the unrecrystallized region, and there is no internal oxidation, and Si, Mn, etc. diffuse to the surface of the steel sheet to form oxides, so there is a drawback that the plating quality is inferior. On the other hand, when it exceeds 900°C, there is a limit to increasing the temperature of the steel sheet due to the limit of the heat treatment equipment, and there is a drawback that a steel sheet with excellent material cannot be obtained by secondary recrystallization.

[0033] Thereafter, the soaked substrate steel sheet is immersed in a molten zinc plating bath at 440 to 460°C to obtain a hot-dip galvanized steel sheet. When the temperature of the molten zinc plating bath is less than 440°C, the viscosity of the plating bath increases, the mobility of the roll for winding the steel sheet decreases, and slip between the steel sheet and the roll may be induced, inducing defects in the steel sheet. When it exceeds 460°C, the phenomenon of the steel sheet dissolving in the plating bath is promoted, and the generation of dross in the form of Fe-Zn compounds is accelerated, which may induce surface defects.

[0034] On the other hand, after the step of obtaining the hot-dip galvanized steel sheet, an alloying heat treatment step of the hot-dip galvanized steel sheet at 480 to 600 °C can be further included. When the alloying heat treatment temperature is less than 480 °C, Fe in the base material may not sufficiently diffuse into the plating layer, and it may not be possible to sufficiently ensure the Fe content in the plating layer. When it exceeds 600 °C, the Fe content in the plating layer becomes excessive, and a powdering phenomenon may occur in which the plating layer peels off during the process of processing the steel sheet.

Example

[0035] Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are illustrative for explaining the present invention in more detail and do not limit the scope of rights of the present invention.

[0036] (Example) A molten metal having the alloy composition shown in Table 1 below was produced into an ingot with a width of 175 mm and a thickness of 90 mm in a vacuum melting furnace, then reheated at 1200 °C for 1 hour for homogenization treatment, hot finish rolled at 900 °C which is a temperature of Ar3 or higher, and then held at 680 °C for 1 hour to simulate hot rolling coiling. Thereafter, the hot rolled steel sheet was immersed in a pickling solution of 15% HCl for 40 seconds to simulate the pickling process. Thereafter, cold rolling was performed at a cold reduction rate of 50 to 60% to produce a cold rolled steel sheet. This cold rolled steel sheet was subjected to soaking heat treatment in a gas atmosphere of 5% H + 95% N having the dew point temperature conditions shown in Table 2 below in a reduction furnace at 800 °C, then cooled, immersed in a hot-dip galvanizing bath at 460 °C for 5 seconds, and then the plating adhesion amount was adjusted to a level of 60 g / m 2 on a single-sided basis by air wiping to produce a hot-dip galvanized steel sheet.

[0037] For the hot-dip galvanized steel sheet produced in this way, after measuring the mechanical properties, the thickness of the internal oxide layer, the plating property, the decarburization rate, and the maximum length of the LME crack, the results are shown in Table 2 below. On the other hand, the measured oxide was an Al, Si composite oxide.

[0038] The mechanical properties were measured as follows: The hot-dip galvanized steel sheet was cut into a size of 40 mm × 200 mm in the direction perpendicular to the rolling direction, and after the side surfaces were milled and ground, a tensile test piece was prepared according to JIS No. 5 standard, and the yield strength (YS), tensile strength (TS), and elongation (EL) were measured with a tensile testing machine.

[0039] The thickness of the internal oxidation layer was measured at a magnification of 5000 by arbitrarily selecting 10 locations from the micrograph of the cross-section obtained by a scanning electron microscope (SEM), and the average value was described.

[0040] The plating property was evaluated by measuring the formation area fraction of the hot-dip galvanized layer with respect to the total area of the hot-dip galvanized steel sheet by image analysis, and by applying a structural adhesive onto the hot-dip galvanized steel sheet, curing it at 175 °C for 20 minutes, and then checking whether or not it adheres to the sealer (plating adhesion) when bent at 90° (bending).

[0041] The decarburization rate was measured by measuring the C profile on the GDOES (Glow Discharge Optical Emission Spectroscopy) depth profile up to about 50 μm in the depth direction of the base steel sheet, and then measuring the fraction of the depleted region with respect to the total area on the above profile.

[0042] The maximum length of the LME crack was measured by laminating the steel sheets, passing a welding current using a Cu-Cr electrode with a tip diameter of 6 mm, welding under the conditions of a welding current time of 16 cycles and a holding time of 15 cycles with a pressing force of 2.6 kN, and then observing and measuring the cross-section of the inclined portion of the area boundary where the electrode of the welding rod contacts the steel sheet with an optical microscope.

[0043] [Table 1]

[0044] [Table 2]

[0045] As can be seen from Tables 1 and 2 above, in the case of Invention Examples 1 to 4 that satisfy the alloy compositions and production conditions proposed by the present invention, since the thickness of the internal oxide layer and the decarburization rate to be obtained by the present invention are ensured, it can be seen that they have excellent plating properties and LME crack resistance.

[0046] On the other hand, Comparative Examples 1 and 3 are not only lower than Al / Si proposed by the present invention, but also cannot ensure the thickness of the internal oxide layer and the decarburization rate proposed by the present invention due to a very low dew point temperature, so it can be seen that they are inferior in plating adhesion and LME crack resistance.

[0047] Comparative Example 2 not only exceeds Al / Si proposed by the present invention, but also cannot ensure the thickness of the internal oxide layer and the decarburization rate proposed by the present invention due to a very low dew point temperature, so unplated areas occur, and it can be seen that it is also inferior in plating adhesion and LME crack resistance.

[0048] Comparative Example 4 does not satisfy the total of Si and Al proposed by the present invention, so the elongation rate is at a low level, and since the decarburization rate proposed by the present invention cannot be ensured due to a low dew point temperature, it can be seen that it is inferior in LME crack resistance.

[0049] Comparative Example 5 satisfies the alloy composition proposed by the present invention, but since the decarburization rate proposed by the present invention cannot be ensured due to a low dew point temperature, it can be seen that it is inferior in LME crack resistance.

[0050] Figure 1 is a photograph of Invention Example 1, where (a) is a surface photograph and (b) is a photograph after the plating adhesion test. Figure 2 is a photograph of Comparative Example 3, where (a) is a surface photograph and (b) is a photograph after the plating adhesion test. As can be seen from Figures 1 and 2, Invention Example 1 has almost no unplated areas and no peeling of the plating layer, and the plating quality is good, while Comparative Example 3, although having almost no unplated areas, has peeling of the plating layer, and it can be seen that the plating quality is inferior.

[0051] Figure 3 is a photograph of Invention Example 1 observed by SEM. As can be seen from Figure 3, it can be seen that in Invention Example 1, an internal oxide layer containing intermittently present oxides is formed to an appropriate thickness.

Claims

1. A hot-dip galvanized steel sheet having a base steel sheet and a hot-dip galvanized layer formed on one or both surfaces of the base steel sheet, wherein the base steel sheet contains, by weight %, carbon (C): 0.1 to 0.3%, silicon (Si): 0.1 to 2.0%, aluminum (Al): 0.1 to 1.5%, manganese (Mn): 1.5 to 3.0%, the balance being Fe and unavoidable impurities, the total of Si and Al satisfies 1.2 to 3.5%, and the ratio of Al to Si (Al / Si) satisfies 0.5 to 2.0, the base steel sheet contains an internal oxide layer having a thickness of 1 to 5 μm immediately below the surface, a high-strength hot-dip galvanized steel sheet excellent in plating adhesion and weldability, wherein the decarburization rate in the region from immediately below the surface of the base steel sheet to 50 μm is 50% or more.

2. The high-strength hot-dip galvanized steel sheet excellent in plating adhesion and weldability according to claim 1, wherein the internal oxide layer contains an oxide composed of an Al, Si composite oxide.

3. The high-strength hot-dip galvanized steel sheet excellent in plating adhesion and weldability according to claim 2, wherein the oxide is present discontinuously.

4. The high-strength hot-dip galvanized steel sheet excellent in plating adhesion and weldability according to claim 1, wherein the hot-dip galvanized steel sheet has a yield strength of 600 MPa or more, a tensile strength of 950 MPa or more, and an elongation of 20% or more.

5. The high-strength hot-dip galvanized steel sheet excellent in plating adhesion and weldability according to claim 1, wherein the area of the hot-dip galvanized layer with respect to the total area of the base steel sheet is 95% or more.

6. The high-strength hot-dip galvanized steel sheet excellent in plating adhesion and weldability according to claim 1, wherein the maximum length of the LME crack is 50 μm or less, and the maximum length of the LME crack is measured by observing a cross-section with an optical microscope at the inclined portion of the area boundary where the electrode of the welding rod contacts the steel sheet after welding is performed under the conditions of a welding current flowing using a Cu—Cr electrode having a tip diameter of 6 mm, a energization time of 16 cycles, and a holding time of 15 cycles with a pressing force of 2.6 kN after the steel sheets are laminated.

7. A method for manufacturing the high-strength hot-dip galvanized steel sheet excellent in plating adhesion and weldability according to claim 1, wherein By weight, carbon (C): 0.1 to 0.3%, silicon (Si): 0.1 to 2.0%, aluminum (Al): 0.1 to 1.5%, manganese (Mn): 1.5 to 3.0%, the balance being Fe and unavoidable impurities, the total of said Si and Al satisfies 1.2% or more, and the ratio of said Al and Si (Al / Si) satisfies 0.5 to 2.0, preparing a base steel sheet; Soaking the base steel sheet in a gas atmosphere having a dew point temperature of 10 to 20°C and containing 3 to 20% hydrogen, the balance being nitrogen and other unavoidable impurities, in a temperature range of 750 to 900°C; Dipping the soaked base steel sheet into a molten zinc plating bath at 440 to 460°C to obtain a hot-dip galvanized steel sheet, a method for manufacturing a high-strength hot-dip galvanized steel sheet excellent in plating adhesion and weldability.

8. The step of preparing the base steel sheet includes reheating a slab at 1000 to 1300°C, hot finish rolling the reheated slab at 800 to 950°C to obtain a hot-rolled steel sheet, winding the hot-rolled steel sheet at 630 to 700°C, pickling the wound hot-rolled steel sheet, and then cold rolling to obtain a cold-rolled steel sheet, a method for manufacturing a high-strength hot-dip galvanized steel sheet excellent in plating adhesion and weldability according to Claim 7.

9. After the step of obtaining the hot-dip galvanized steel sheet, further including a step of subjecting the hot-dip galvanized steel sheet to an alloying heat treatment at 480 to 600°C, a method for manufacturing a high-strength hot-dip galvanized steel sheet excellent in plating adhesion and weldability according to Claim 7.

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