Plated steel with excellent workability and corrosion resistance

Abstract

The present invention provides a plated steel material having excellent workability and corrosion resistance, comprising: a base iron; and a hot-dip alloy-plated layer formed on the base iron; the hot-dip alloy-plated layer containing, by weight, 5% to 30% Al, 2% to 10% Mg, the balance Zn, and other unavoidable impurities, an area fraction of an MgZn2 phase in a cross section of the hot-dip alloy-plated layer being 20 to 70%, and a ratio of an area fraction of an Al-containing phase to the area fraction of the MgZn2 phase being 1 to 70%.

Description

[Technical Field]

[0001] The present invention relates to a steel material, and more particularly to a plated steel material having excellent workability and corrosion resistance. [Background technology]

[0002] Hot-dip galvanized steel sheets have excellent sacrificial corrosion protection properties. When exposed to a corrosive environment, zinc, which has a lower potential, dissolves first, preventing corrosion of the steel. Due to these excellent corrosion properties, hot-dip galvanized steel sheets are used in home appliances, building materials, and automobiles. However, as technological advances and quality standards have led to higher expectations for corrosion resistance, there has been a growing need to develop products with better corrosion resistance than conventional hot-dip galvanized steel sheets. To address this issue, since the early 2000s, Europe and Japan have been producing highly corrosion-resistant coated steel sheets by adding aluminum (Al) and magnesium (Mg) to the zinc (Zn) plating bath. In addition to the sacrificial corrosion protection properties of Zn, the addition of Mg and Al forms dense corrosion products in corrosive environments, insulating the steel from oxidizing atmospheres and improving corrosion resistance. However, while Zn-Al-Mg coated steel sheets have superior corrosion resistance compared to galvanized steel sheets, they suffer from poor formability. Zn-Al-Mg intermetallic compounds have low crack resistance due to their high hardness, and such cracks can damage the appearance during processing or expose the base steel material, resulting in reduced corrosion resistance. Related prior art includes Japanese Patent Publication No. 2005-105367. Summary of the Invention [Problem to be solved by the invention]

[0003] The technical problem to be achieved by the present invention is to provide a plated steel material that is excellent in workability and corrosion resistance. [Means for solving the problem]

[0004] In order to solve the above problems, one aspect of the present invention provides a plated steel material having excellent workability and corrosion resistance, comprising: a base iron; and a hot-dip alloy plating layer formed on the base iron; wherein the hot-dip alloy plating layer contains, by weight, 5% to 30% Al, 2% to 10% Mg, the balance being Zn, and other unavoidable impurities, and the area fraction of an MgZn2 phase in a cross section of the hot-dip alloy plating layer is 20 to 70%, and the ratio of the area fraction of an Al-containing phase to the area fraction of the MgZn2 phase in a cross section of the hot-dip alloy plating layer is 1 to 70%.

[0005] According to another aspect of the present invention for solving the above-mentioned problems, there is provided a plated steel material having excellent workability and corrosion resistance, comprising: a base iron; and a hot-dip alloy plating layer formed on the base iron; wherein the hot-dip alloy plating layer contains, by weight, 5% to 30% Al, 2% to 10% Mg, the balance being Zn, and other unavoidable impurities, and the hot-dip alloy plating layer has an area fraction of 70% or less of an MgZn2 phase at its surface, the MgZn2 phase having a ratio of an average minor axis length (a) to an average major axis length (b) of 0.5 or less among all the MgZn2 phases.

[0006] In the plated steel material having excellent workability and corrosion resistance, the MgZn2 phase having a ratio of the average minor axis length (a) to the average major axis length (b) of 0.5 or less may have a ratio of the average minor axis length (a) to the average major axis length (b) of 1 / 10 or more and 1 / 2 or less.

[0007] In the plated steel material having excellent workability and corrosion resistance, the average minor axis length (a) may be 1 to 20 μm, and the average major axis length (b) may be 2 to 200 μm.

[0008] In the plated steel material having excellent workability and corrosion resistance, the hot-dip alloy plating layer may have an area fraction of Al-Zn dendrites composed of Al phase and Zn phase on the surface of 30% or less.

[0009] In the plated steel material having excellent workability and corrosion resistance, the hot-dip alloy plating layer may have an area fraction of MgZn2 phases at the surface, the area fraction of which has a ratio of an average minor axis length (a) to an average major axis length (b) exceeding 0.5 in the entire MgZn2 phase.

[0010] In the plated steel material having excellent workability and corrosion resistance, the diameter of an imaginary circle having the same area as the cross-sectional area of ​​the MgZn2 phase having a ratio of the average minor axis length (a) to the average major axis length (b) exceeding 0.5 may be 1 to 50 μm.

[0011] In the plated steel material having excellent workability and corrosion resistance, the hot-dip alloy plating layer may further contain, by weight, Fe: 0.05% to 10% and Si: more than 0 and less than 1%. [Effects of the Invention]

[0012] According to an embodiment of the present invention, a plated steel material having excellent workability and corrosion resistance can be realized.

[0013] It goes without saying that the scope of the present invention is not limited by such effects. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a photograph of the surface of a hot-dip alloy plating layer according to Example 2 in the first experimental example. [Figure 2] 1 is a photograph of a cross section of a hot-dip alloy plating layer according to Example 2 in a first experimental example, taken with an FE-SEM at a magnification of 1000 times. [Figure 3] 1 is a photograph of a processed portion of a hot-dip alloy plating layer according to Example 2 in a first experimental example, taken with an FE-SEM at a magnification of 500 times after evaluation of 1T bending workability. DETAILED DESCRIPTION OF THE INVENTION

[0015] A plated steel sheet with excellent workability and corrosion resistance according to one embodiment of the present invention will now be described in detail. The terms used below have been appropriately selected in consideration of the functions of the present invention, and the definitions of these terms should be based on the overall content of this specification. Below, we will provide specific details of an ultra-high strength, highly corrosion-resistant plated steel sheet with excellent elongation and a method for manufacturing the same.

[0016] As mentioned above, Zn-Al-Mg coated steel sheets have superior corrosion resistance compared to galvanized steel sheets, but have the disadvantage of inferior formability. The Zn-Al-Mg intermetallic compound has low crack resistance due to its high hardness, and such cracks can damage the appearance during processing or expose the base steel, reducing corrosion resistance during processing. Because MgZn2 has the highest hardness among intermetallic compounds, technology to control the shape and size of the MgZn2 phase is important.

[0017] The present invention relates to a Zn-Al-Mg-based highly corrosion-resistant plated steel material containing, by weight, 5% to 30% Al, 2% to 10% Mg, the balance being Zn, and other unavoidable impurities, and aims to control the microstructure of the high-hardness MgZn2 phase in order to improve workability and working corrosion resistance.

[0018] A plated steel material having excellent workability and corrosion resistance according to one embodiment of the present invention includes a base steel and a hot-dip alloy coating layer formed on the base steel, the hot-dip alloy coating layer containing, by weight, 5% to 30% Al, 2% to 10% Mg, the balance Zn, and other inevitable impurities. The hot-dip alloy coating layer may further contain, by weight, 0.05% to 10% Fe and more than 0% but less than 1% Si.

[0019] The zinc alloy plating layer of the present invention is a primary crystal Al phase (a single-phase structure of Al with Zn solid solution), a Zn solid solution phase, MgZn2 (MgZn2 phase containing Al, Mg2Zn 11In terms of the microstructure for improving workability and corrosion resistance during processing, the MgZn2 phase and the MgZn2 phase containing Al on the surface of the Zn-Al-Mg based coating layer may have polygonal, rod-like, and needle-like shapes.

[0020] The zinc alloy coating layer may be composed of, by weight, 5% to 30% Al, 2% to 10% Mg, the remainder Zn, and unavoidable impurities. Mg and Al in the coating layer are elements that improve corrosion resistance, and they enhance corrosion resistance by forming denser corrosion products. Mg content less than 1.0 wt.% contributes little to corrosion resistance. Conventionally, Mg content exceeding 2.0 wt.% has been used because production difficulties due to Mg oxide dross have been observed. However, in the present invention, Mg is added in an amount of 2.0 wt.% or more to achieve better corrosion resistance. As mentioned above, Mg content exceeding 2.0 wt.% can cause production difficulties due to oxide dross, but adding Al in an amount of 5.0 wt.% or more can reduce dross due to Mg oxidation in the molten metal. Furthermore, the addition of Al can improve corrosion resistance by forming primary Al crystals and a Zn-Al-Mg ternary eutectic phase. On the other hand, when Mg is added in excess of 10.0 wt%, the rod- and needle-shaped MgZn2 or Al-containing MgZn2 phase grows to an area fraction exceeding 70% of the total MgZn2, resulting in poor formability of the coating layer and reduced corrosion resistance due to cracks in the coating layer during processing, exposing the steel or the Fe-Al-Zn interfacial alloyed layer.On the other hand, when Al is added in excess of 30 wt%, the melting point of the coating bath increases, causing excessive growth of a discontinuous Fe-Al-Zn interfacial alloyed layer between the steel and the coating layer, which can weaken interfacial adhesion during processing.

[0021] In the present invention, an exemplary process for forming a hot-dip alloy plating layer on a base steel is as follows.

[0022] First, the base steel is annealed at 680 to 850°C, immersed in a plating bath at 440 to 530°C, and then passed through an air knife to coat the steel with a coating of 30 to 300 g / m² on one side.2 However, the entry temperature of the annealed base steel must be adjusted so that it does not differ by more than ±20°C from the temperature of the plating bath.

[0023] The shape and fraction of the MgZn2 phase can be precisely controlled by cooling. By cooling at a rate of 3 to 30°C / s from immersion in the coating bath until the temperature reaches 200°C, the shape of the phase generated during solidification of the coating layer can be controlled. More preferably, cooling can be performed at a rate of 5 to 20°C / s. If the cooling rate is less than 5°C / s, the primary MgZn2 phase will grow coarsely, resulting in poor workability, and the liquid coating layer may react with oxygen, impairing the appearance of the coating surface. In contrast, cooling at a rate exceeding 30°C / s has the disadvantages of uneven solidification resulting in an inconsistent coating layer and reduced productivity due to sheet vibration.

[0024] A plated steel material according to one aspect of the present invention is characterized in that the area fraction of the MgZn2 phase in a cross section (e.g., a vertical section) in the hot-dip alloy coating layer is 20 to 70%, and the ratio of the area fraction of the Al-containing phase to the area fraction of the MgZn2 phase in a cross section (e.g., a vertical section) in the hot-dip alloy coating layer is 1 to 70%. Here, the Al-containing phase may be present separated from the MgZn2 phase or present within the MgZn2 phase in the cross section in the hot-dip alloy coating layer. In this embodiment, the Al-containing phase refers to i) a single Al phase, or ii) a phase containing 20% ​​or more Al, unavoidable impurities of 2% or less, and the remainder being Zn.

[0025] For example, the hot-dip alloy coating layer contains an MgZn2 phase at an area fraction of 20 to 70% in a cross section. That is, the proportion of the cross-sectional area (A2) occupied by the MgZn2 phase in the total cross-sectional area (A1) of the hot-dip alloy coating layer is 20 to 70%, and the value of (A2 / A1) × 100 satisfies the range of 10 to 60. Meanwhile, in the cross section of the hot-dip alloy coating layer, the sum of the cross-sectional area (B1) of the Al-containing phase present apart from the MgZn2 phase and the cross-sectional area (B2) of the Al-containing phase present inside the MgZn2 phase accounts for 1 to 70% of the cross-sectional area (B3) of the total MgZn2 phase. That is, the value of [(B1 + B2) / B3] × 100 satisfies the range of 1 to 70. Such a structure has excellent crack resistance; specifically, the average crack width in bending tests (3T bending test, 1T bending test) may be 30 μm or less.

[0026] The hot-dip alloy plating layer of the plated steel material of the present invention may have an area fraction of the MgZn2 phase at the surface of 10 to 70%, and an area fraction of less than 10% is impossible to form, while an area fraction exceeding 70% reduces crack resistance. Here, the surface of the hot-dip alloy plating layer may refer to the upper surface that comes into contact with the outside.

[0027] In another embodiment of the present invention, the hot-dip alloy plating layer of the plated steel material may have an area fraction of 70% or less of MgZn2 phases at the surface, the ratio of the average minor axis length (a) to the average major axis length (b) being 0.5 or less. For example, 70% or less of the MgZn2 phases at the surface of the hot-dip alloy plating layer may have a ratio of the average minor axis length (a) to the average major axis length (b) of 1:2 to 1:10, which is 0.5 or less. In this case, the ratio of the average minor axis length (a) to the average major axis length (b) of the MgZn2 phases having a ratio of 0.5 or less may be 1 / 10 or more and 1 / 2 or less. If the ratio of the average minor axis length (a) to the average major axis length (b) is less than 0.5, crack resistance is reduced. The average minor axis length (a) may be 1 to 20 μm, and the average major axis length (b) may be 2 to 200 μm. An average minor axis length (a) of less than 1 μm and an average major axis length (b) of less than 2 μm are impossible to form, and if the average minor axis length (a) exceeds 20 μm or the average major axis length (b) exceeds 200 μm, crack resistance decreases.

[0028] On the other hand, in the hot-dip alloy coating layer of the coated steel material according to another aspect of the present invention, the area fraction of Al-Zn dendrites composed of Al and Zn phases on the surface may be 30% or less. Since Al-Zn dendrites have an unfavorable effect on chemical conversion treatability and LME (liquid metal embrittlement) resistance, it is preferable that their area fraction is low. Therefore, in the coating layer according to this embodiment, the area fraction of Al-Zn dendrites is set to 30% or less.

[0029] As described above, in a plated steel material with excellent workability and corrosion resistance according to one embodiment of the present invention, the MgZn2 phase and the Al-containing MgZn2 phase on the surface of the Zn-Al-Mg-based coating layer are characterized in that they are composed of polygonal, rod-like, and needle-like shapes, and the ratio of the average minor axis length (a) to the average major axis length (b) of the rod-like and needle-like shapes is 1:2≦a:b≦1:10. Of the total MgZn2, the rod- and needle-like MgZn2 phase is distributed on the surface at an area fraction of 70% or less, more preferably at an area fraction of less than 50%, and the remainder MgZn2 is distributed in polygonal shapes.

[0030] The hot-dip alloy plating layer is characterized in that the area fraction of MgZn2 phases at the surface, in which the ratio of the average minor axis length (a) to the average major axis length (b) exceeds 0.5, is 30% or more. For example, the hot-dip alloy plating layer is characterized in that 30% or more of the MgZn2 phases at the surface, in which the ratio of the average minor axis length (a) to the average major axis length (b) exceeds 0.5, is 1:1.5, 1:1.2, or the like. The diameter (average diameter) of a virtual circle having the same area as the cross-sectional area of ​​the MgZn2 phases having the ratio of the average minor axis length (a) to the average major axis length (b) exceeding 0.5, may be 1 to 50 μm. An average diameter of less than 1 μm is impossible to form, and an average diameter exceeding 50 μm results in reduced crack resistance.

[0031] Preferred experimental examples are presented below to aid in understanding the present invention, but the following experimental examples are merely provided to aid in understanding the present invention and are not intended to limit the present invention.

[0032] First experimental example 1. Test specimen composition and process conditions A 1.2 mm cold-rolled steel sheet was prepared as the base steel sheet. Its composition was 0.15 wt% carbon (C), 0.01 wt% silicon (Si), 0.6 wt% manganese (Mn), 0.05 wt% phosphorus (P), 0.05 wt% sulfur (S), and the remainder iron (Fe). After annealing at 760°C in a nitrogen-5-10% hydrogen atmosphere, the annealed specimen was cooled to a temperature no more than 20°C different from the coating bath temperature and then immersed in the coating bath for 1-5 seconds. After immersion in a 485°C coating bath, the coating thickness was adjusted to approximately 20 μm using nitrogen wiping, and the specimen was cooled at a cooling rate of 7°C / s to obtain a Zn-Al-Mg-based coated steel sheet. The coating bath composition, by weight, was 5-30% Al, 2-10% Mg, and the remainder Zn.

[0033] 2. Evaluation of the composition and microstructure of the plating layer Table 1 shows the results of evaluating the composition (unit: wt %) and microstructure of the hot-dip alloy coating layer in the plated steel material according to the first experimental example of the present invention.

[0034] [Table 1]

[0035] For each plated steel sheet produced, the area of ​​the rods and needle-shaped MgZn2 was measured using an image program after observing the surface with a FE-SEM at a magnification of 500x. The thickness of the interfacial alloy layer was measured at a cross section magnified at 1000x.

[0036] Referring to Examples 1 to 3 in Table 1, it can be seen that the area ratio of rod and needle-shaped MgZn2 is less than 50%, which indicates excellent workability. As comparative examples to the examples, the inventors confirmed that the area of ​​rod and needle-shaped MgZn2 phases increases sharply, and that an interface alloy layer exceeding 10 μm is formed due to an increase in the temperature of the plating bath, resulting in poor workability.

[0037] Figure 1 is a photograph of the surface of the hot-dip alloy coating layer according to Example 2 in Experimental Example 1. Referring to Figure 1, it can be seen that the rod- and needle-shaped MgZn2 phases on the surface of the Zn-Al-Mg coating layer have an average minor axis length (a) to average major axis length (b) ratio that satisfies the range of 1:2≦a:b≦1:10. It can also be seen that the rod- and needle-shaped MgZn2 phases are distributed on the surface at an area fraction of 70% or less of the total MgZn2 phases.

[0038] Fig. 2 is a photograph of the cross section of the hot-dip alloy coating layer according to Example 2 in Experimental Example 1, taken with an FE-SEM at a magnification of 1000. Referring to Fig. 2, it can be seen that the growth of the Fe-Al interfacial alloy layer in the hot-dip alloy coating layer according to Example 2 is 10 µm or less.

[0039] 3. Evaluation of bending workability Table 2 shows the results of evaluating the bending workability of plated steel materials according to the first experimental example of the present invention. After 3T bending and 1T bending, the bent sections were observed with a field emission scanning electron microscope (FE-SEM) at magnifications of 200x and 500x, and the widths of the cracks on the bends were measured and averaged for evaluation. For 3T (crack width) and 1T (crack width), a "◎" indicates that the average crack width in the bending evaluation was 15 μm or less, a "○" indicates that the average crack width in the bending evaluation was more than 15 μm and less than or equal to 30 μm, and a "△" indicates that the average crack width in the bending evaluation was more than 30 μm and less than or equal to 40 μm.

[0040] After 3T and 1T bending, the bent section was observed at 100x magnification using a field emission scanning electron microscope (FE-SEM), and the crack area fraction was calculated and evaluated using an image program. For 3T (crack area fraction) and 1T (crack area fraction), a "◎" indicates that the crack area fraction in the bending evaluation was 30% or less, a "○" indicates that the crack area fraction in the bending evaluation was more than 30% and less than 50%, and a "△" indicates that the crack area fraction in the bending evaluation was more than 50% and less than 70%.

[0041] [Table 2]

[0042] Referring to Examples 1 to 3 in Table 2, it can be seen that the formation of rod- and needle-shaped MgZn2 is relatively small, and the crack width is within 40 μm. As a comparative example to the Examples, the inventors confirmed that when the area fraction of rod- and needle-shaped MgZn2 exceeds 70%, cracks not only occur in the MgZn2 phase, which has high hardness, but also progress along grain boundaries, resulting in an average crack width exceeding 40 μm. Furthermore, as a comparative example to the Examples, the inventors confirmed that when the MgZn2 phase develops into rods, not only the crack width but also the frequency of cracks increases, and the crack area exceeds 70%, resulting in poor cracking. Figure 3 is a 500x FE-SEM photograph of the processed portion of the hot-dip alloy coating layer according to Example 2 in the first experimental example after evaluating 1T bending workability. Referring to FIG. 3, it can be seen that in the hot-dip alloy coating layer according to Example 2, the formation of rod- and needle-shaped MgZn2 is relatively small, the crack width is within 40 μm, and the area fraction of rod- and needle-shaped MgZn2 is 70% or less.

[0043] The results of the above-described first experimental example confirm that even if the MgZn2 phase, which has high hardness and is disadvantageous to formability, is formed, it is possible to realize a plated steel sheet with excellent formability by suppressing the growth of the rod- and needle-like MgZn2 phases and adjusting their area fractions.

[0044] Second Experimental Example 1. Test specimen composition and process conditions A 1.2 mm cold-rolled steel sheet was prepared as the base steel sheet. Its composition was 0.15 wt% carbon (C), 0.01 wt% silicon (Si), 0.6 wt% manganese (Mn), 0.05 wt% phosphorus (P), 0.05 wt% sulfur (S), and the remainder iron (Fe). After annealing at 760°C in a nitrogen-5-10% hydrogen atmosphere, the annealed specimen was cooled to a temperature no more than 20°C different from the coating bath temperature and then immersed in the coating bath for 1-5 seconds. After immersion in a 485°C coating bath, the coating thickness was adjusted to approximately 20 μm using nitrogen wiping, and the specimen was cooled at a cooling rate of 7°C / s to obtain a Zn-Al-Mg-based coated steel sheet. The coating bath composition, by weight, was 5-30% Al, 2-10% Mg, and the remainder Zn. The hot-dip alloy coating layer contains 5 wt % or more and 30 wt % or less of Al, 2 wt % or more and 10 wt % or less of Mg, 0.05 wt % or more and 10 wt % or less of Fe, more than 0 wt % and less than 1 wt % of Si, and the remainder being Zn and other components diffused from the base iron.

[0045] 2. Evaluation of the cross-sectional microstructure of the coating layer and bending workability Table 3 shows the results of evaluation of bending workability in plated steel materials according to a second experimental example of the present invention, as a function of the area fraction (%) of the MgZn2 phase in the cross section of the hot-dip alloy coating layer and the area ratio (%) of the Al single phase to the area fraction of the MgZn2 phase in the cross section of the hot-dip alloy coating layer. In Table 3, bending workability was evaluated by observing the bent portion after 3T bending with a field emission scanning electron microscope (FE-SEM) at magnifications of 200x and 500x, measuring the width of bending cracks, and then averaging the measured values. An "O" indicates that the average crack width in the bending evaluation was greater than 0 and less than or equal to 30 μm, and an "X" indicates that the average crack width in the bending evaluation was greater than 30 μm.

[0046] [Table 3]

[0047] Referring to Table 3, it can be confirmed that Test Specimens 1, 2, 3, and 4 correspond to cases in which the area fraction of the MgZn2 phase in the cross section of the hot-dip alloy coating layer satisfies the range of 20 to 70%, and the ratio of the area fraction of the Al-containing phase to the area fraction of the MgZn2 phase satisfies the range of 1 to 70%, and that the average crack width in the bent portion after 3T bending is 30 μm or less in all cases.

[0048] In contrast, test piece 5 corresponds to a case where the area fraction of the MgZn2 phase in the cross section of the hot-dip alloy coating layer does not satisfy the range of 20 to 70%, and test pieces 6, 7, and 8 correspond to a case where the ratio of the area fraction of the Al-containing phase to the area fraction of the MgZn2 phase in the cross section of the hot-dip alloy coating layer does not satisfy the range of 1 to 70%, and in these cases, it can be confirmed that the average crack width in the bent portion after T-bending exceeds 30 μm.

[0049] [Table 4]

[0050] Table 4 shows the results of evaluation of bending workability according to the area fraction (%) of the MgZn2 phase on the surface of the hot-dip alloy coating layer and the ratio of the average minor axis length (a) to the average major axis length (b) for coated steel materials according to the second experimental example of the present invention. Case 1 relates to MgZn2 in which the ratio of the average minor axis length (a) to the average major axis length (b) among all MgZn2 on the surface of the coating layer exceeds 0.5, and Case 2 relates to MgZn2 in which the ratio of the average minor axis length (a) to the average major axis length (b) among all MgZn2 on the surface of the coating layer is 0.5 or less. The bending workability in Table 4 was evaluated using a coated steel sheet in which the area fraction of MgZn2 in the cross section of the coating layer was 20 to 70%, and an Al-containing phase, present within the MgZn2 phase or separated from the MgZn2 phase, accounted for 1 to 70% of the cross section of the MgZn2 phase. In this evaluation, the bending workability was evaluated by observing the bent portion after 3T bending at magnifications of 200x and 500x with a field emission scanning electron microscope (FE-SEM), measuring the widths of bending cracks, and averaging the measured values. A "◎" indicates that the average crack width in the 3T bending evaluation was greater than 0 and not more than 15 μm, and a "○" indicates that the average crack width in the 3T bending evaluation was greater than 15 μm and not more than 30 μm. Referring to Table 4, it can be confirmed that test specimens A1, A2, B1, B2, C1, and C2 satisfy all of the following conditions: the area fraction of the MgZn2 phase, in which the ratio of the average minor axis length (a) to the average major axis length (b) exceeds 0.5, is 30% or more, the area fraction of the MgZn2 phase, in which the ratio of the average minor axis length (a) to the average major axis length (b) is 0.5 or less, is 70% or less, the ratio of the average minor axis length (a) to the average major axis length (b) is 1 / 10 or more and 1 / 2 or less, the average minor axis length (a) is 1 to 20 μm, and the average major axis length (b) is 2 to 200 μm, and in these cases, the average crack width in the 3T bending test was 15 μm or less.

[0051] In contrast, test pieces D1, D2, D3, D4, and D5 are cases in which the area fraction of the MgZn2 phase, in which the ratio of the average minor axis length (a) to the average major axis length (b) exceeds 0.5 in the entire MgZn2 phase on the surface of the hot-dip alloy coating layer, does not satisfy the range of 30% or more, and the area fraction of the MgZn2 phase, in which the ratio of the average minor axis length (a) to the average major axis length (b) is 0.5 or less in the entire MgZn2 phase on the surface of the hot-dip alloy coating layer, does not satisfy the range of 70% or less, and in these cases, it can be confirmed that the average crack width in the 3T bending evaluation exceeds 15 μm.

[0052] Furthermore, test pieces A3, B3, C3, and D5 are cases in which the ratio of the average minor axis length (a) to the average major axis length (b) within the entire MgZn2 phase on the surface of the hot-dip alloy coating layer does not satisfy the range of 1 / 10 or more and 1 / 2 or less, and in these cases, it can be confirmed that the average crack width in the 3T bending evaluation exceeds 15 μm.

[0053] Furthermore, in test pieces A4, B4, and C4, the area fraction of the MgZn2 phase, in which the ratio of the average minor axis length (a) to the average major axis length (b) is 0.5 or less among all the MgZn2 phases on the surface of the hot-dip alloy plating layer, is 70% or less, and even if the ratio of the average minor axis length (a) to the average major axis length (b) among all the MgZn2 phases on the surface of the hot-dip alloy plating layer satisfies the range of 1 / 10 or more and 1 / 2 or less, the average minor axis length (a) does not satisfy the range of 1 to 20 μm, and in this case, it can be confirmed that the average crack width in the 3T bending evaluation exceeds 15 μm.

[0054] Furthermore, in test pieces A5, B5, and C5, the area fraction of the MgZn2 phase, in which the ratio of the average minor axis length (a) to the average major axis length (b) is 0.5 or less among all the MgZn2 phases on the surface of the hot-dip alloy plating layer, is 70% or less, and even if the ratio of the average minor axis length (a) to the average major axis length (b) among all the MgZn2 phases on the surface of the hot-dip alloy plating layer satisfies the range of 1 / 10 or more and 1 / 2 or less, the average major axis length (b) does not satisfy the range of 2 to 200 μm, and in this case, it can be confirmed that the average crack width in the 3T bending evaluation exceeds 15 μm.

[0055] Although the present invention has been described above with reference to the preferred embodiments, various modifications and variations may be made by those skilled in the art. Such modifications and variations are within the scope of the present invention. Therefore, the scope of the present invention should be determined by the following claims.

Claims

1. bare iron; and a hot-dip alloy plating layer formed on the base steel; The hot-dip alloy plating layer is composed of, by weight %, Al: 5% to 30%, Mg: 2% to 10%, the balance being Zn and other inevitable impurities, MgZn in the cross section of the hot-dip alloy plating layer ２ The area fraction of the MgZn phase is 20 to 70%. ２ the ratio of the area fraction of the Al-containing phase to the area fraction of the Al-containing phase is 1 to 70%; The hot-dip alloy plating layer is entirely MgZn on the surface. ２ The ratio of the average minor axis length (a) to the average major axis length (b) in the phase is 0.1 or more and 0.5 or less. ２ A plated steel material having excellent workability and corrosion resistance, characterized in that the area fraction of a phase is 30% or more and 70% or less.

2. bare iron; and a hot-dip alloy plating layer formed on the base steel; The hot-dip alloy plating layer is composed of, by weight %, Al: 5% to 30%, Mg: 2% to 10%, the balance being Zn and other inevitable impurities, The hot-dip alloy plating layer is entirely MgZn on the surface. ２ The ratio of the average minor axis length (a) to the average major axis length (b) in the phase is 0.1 or more and 0.5 or less. ２ A plated steel material having excellent workability and corrosion resistance, characterized in that the area fraction of a phase is 30% or more and 70% or less.

3. MgZn having a ratio of the average minor axis length (a) to the average major axis length (b) of 0.5 or less ２ 3. The plated steel material having excellent workability and corrosion resistance according to claim 2, wherein the phase has a ratio of the average minor axis length (a) to the average major axis length (b) of 1 / 10 or more and 1 / 2 or less.

4. 4. The plated steel material having excellent workability and corrosion resistance according to claim 3, wherein the average minor axis length (a) is 1 to 20 μm, and the average major axis length (b) is 2 to 200 μm.

5. 3. The plated steel material having excellent workability and corrosion resistance according to claim 2, wherein the hot-dip alloy plating layer has an area fraction of Al-Zn dendrites composed of an Al phase and a Zn phase on the surface of 30% or less.

6. The ratio of the average minor axis length (a) to the average major axis length (b) exceeds 0.

5. ２ 3. The plated steel material having excellent workability and corrosion resistance according to claim 2, wherein the diameter of an imaginary circle having the same area as the cross-sectional area of ​​the phase is 1 to 50 μm.

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