Highly corrosion-resistant plated steel material and its manufacturing method

Abstract

The present invention provides a highly corrosion-resistant plated steel product having excellent corrosion resistance and a method for manufacturing the same. According to one embodiment of the present invention, a method for manufacturing the highly corrosion-resistant plated steel product includes the steps of immersing a base steel material in a hot-dip alloy coating bath containing, by weight, 6% to 18% aluminum (Al), 3% to 6% magnesium (Mg), and the remainder being zinc (Zn) and other inevitable impurities, withdrawing the immersed base steel material from the hot-dip alloy coating bath to form a hot-dip alloy coating layer on the base steel material, and cooling the base steel material with the hot-dip alloy coating layer formed thereon, wherein the aluminum:magnesium content ratio in the hot-dip alloy coating bath is in the range of 2:1 to 6:1.

Description

[Technical Field]

[0001] The present invention relates to a steel material, and more particularly to a highly corrosion-resistant plated steel material having excellent corrosion resistance and a method for producing the same. [Background technology]

[0002] Hot-dip galvanized steel sheets are widely used in building materials and home appliances due to their excellent self-sacrificing properties. When hot-dip galvanized steel sheets are exposed to a corrosive environment, zinc (Zn) acts as a sacrificial anode in the exposed iron base material, resulting in zinc loss from the coating layer. This sacrificial anode function of zinc effectively prevents rust formation on the iron base material in a corrosive environment, but it also reduces anode efficiency. To address this issue, the addition of magnesium (Mg) to zinc (Zn) has been used to produce dense corrosion products in a corrosive environment, improving anode efficiency and resulting in the production of highly corrosion-resistant plated products with excellent corrosion resistance. However, while the addition of magnesium to zinc increases corrosion resistance, it also reduces the workability of the coating layer and reduces corrosion resistance due to the increase in magnesium oxide. Summary of the Invention [Problem to be solved by the invention]

[0003] The technical problem to be achieved by the technical concept of the present invention is to provide a highly corrosion-resistant plated steel material having excellent corrosion resistance and a method for manufacturing the same, but this problem is merely an example and the technical concept of the present invention is not limited thereto. [Means for solving the problem]

[0004] According to one aspect of the present invention, there are provided a highly corrosion-resistant plated steel material having excellent corrosion resistance and a method for producing the same.

[0005] According to one embodiment of the present invention, the method for producing the highly corrosion-resistant plated steel material includes the steps of immersing a base iron in a hot-dip alloy coating bath containing, by weight, 6% to 18% aluminum (Al), 3% to 6% magnesium (Mg), and the remainder being zinc (Zn) and other inevitable impurities; withdrawing the immersed base iron from the hot-dip alloy coating bath to form a hot-dip alloy coating layer on the base iron; and cooling the base iron with the hot-dip alloy coating layer formed thereon, wherein the aluminum:magnesium content ratio in the hot-dip alloy coating bath may be in the range of 2:1 to 6:1.

[0006] According to one embodiment of the present invention, the hot-dip alloy plating bath may be maintained at a temperature in the range of 420°C to 500°C.

[0007] According to one embodiment of the present invention, the hot-dip alloy plating bath may be maintained at a temperature that is increased by 20°C to 50°C from the melting point of the molten alloy.

[0008] According to an embodiment of the present invention, the cooling step may have a cooling rate of 7° C. / sec to 30° C. / sec.

[0009] According to an embodiment of the present invention, the cooling step may have a cooling rate of 10° C. / sec to 15° C. / sec.

[0010] According to one embodiment of the present invention, the hot-dip alloy plating layer may include a plating base layer and an Fe-Al alloy layer, and the total thickness of the hot-dip alloy plating layer may be at least twice the thickness of the Fe-Al alloy layer.

[0011] According to one embodiment of the present invention, the plating base layer may include a primary Al phase, an Al / Zn eutectoid phase, or both.

[0012] According to an embodiment of the present invention, in the hot-dip alloy coating layer, the primary Al phase, the Al / Zn eutectoid phase, or both of them may have an area fraction in the range of 20% to 60%.

[0013] According to one embodiment of the present invention, the highly corrosion-resistant plated steel material includes: a base iron; and a hot-dip alloy plating layer formed on the base iron, the hot-dip alloy plating layer containing, by weight, 6% to 18% aluminum (Al), 3% to 6% magnesium (Mg), and the balance zinc (Zn) and other unavoidable impurities.

[0014] According to one embodiment of the present invention, the hot-dip alloy coating layer includes a coating base layer and an Fe—Al alloy layer, the coating base layer includes a primary Al phase, an Al / Zn eutectoid phase, or both, and the area fraction of the primary Al phase, the Al / Zn eutectoid phase, or both, in the hot-dip alloy coating layer may be in the range of 20% to 60%.

[0015] According to one embodiment of the present invention, the hot-dip alloy plating layer may include a plating base layer and an Fe-Al alloy layer, and the total thickness of the hot-dip alloy plating layer may be at least twice the thickness of the Fe-Al alloy layer.

[0016] According to an embodiment of the present invention, the aluminum:magnesium content ratio of the hot-dip alloy plating layer may be in the range of 2:1 to 6:1. [Effects of the Invention]

[0017] According to the technical concept of the present invention, a highly corrosion-resistant plated steel material is formed using a hot-dip alloy plating bath containing, by weight, 6% to 18% aluminum (Al), 3% to 6% magnesium (Mg), and the remainder zinc (Zn) and other unavoidable impurities, with an aluminum:magnesium content ratio in the range of 2:1 to 6:1. This produces a primary Al phase or an Al / Zn eutectoid phase, suppressing the formation of an Fe-Al alloy layer and providing excellent corrosion resistance. To ensure sufficient formation of such a primary Al phase or Al / Zn eutectoid phase, the overall thickness of the plating layer must be at least twice that of the alloy layer. The fraction of the primary Al phase or Al / Zn eutectoid phase is preferably 20% to 60% based on the cross section of the hot-dip alloy plating layer, thereby providing excellent corrosion resistance. The above-described effects of the present invention are merely illustrative and are not intended to limit the scope of the present invention. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a process flowchart showing a method for producing a highly corrosion-resistant plated steel material according to an embodiment of the present invention.

[0019] [Figures 2a-2c] 1 is a scanning electron microscope photograph showing the microstructure of a highly corrosion-resistant plated steel material according to an example of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

[0020] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The following examples are provided to more fully explain the technical concept of the present invention to those skilled in the art. The following examples may be modified into various other forms, and the scope of the technical concept of the present invention is not limited to the following examples. Rather, these examples are provided to make the present disclosure more complete and complete, and to fully convey the technical concept of the present invention to those skilled in the art. Throughout this specification, the same reference numerals refer to the same elements. Furthermore, various elements and regions in the drawings are shown schematically. Therefore, the technical concept of the present invention is not limited by the relative sizes and spacings shown in the accompanying drawings. It should be noted that the term "hot-dip alloy plating" hereinafter is used to encompass "hot-dip galvanizing."

[0021] The addition of magnesium to zinc increases the corrosion resistance of hot-dip alloy-coated steel. However, the addition of magnesium can reduce the workability of the coating layer and increase magnesium oxide during manufacturing, so the amount of magnesium added is limited. To minimize these issues, aluminum is added. The addition of aluminum prevents the oxidation of magnesium in the coating bath, improving production stability. At the same time, aluminum forms a primary Al phase or an Al / Zn eutectoid phase in the coating layer, providing excellent corrosion resistance in a variety of environments. Zinc and magnesium, the main components of the coating layer, possess excellent sacrificial protection and provide corrosion resistance through corrosion weight loss in corrosive environments. In contrast, the primary Al or Al / Zn eutectoid phase of the coating layer independently forms a strong passive layer without sacrificial protection, maintaining high structural corrosion resistance in corrosive environments.

[0022] The present invention provides a plated steel material and a manufacturing method thereof that have increased corrosion resistance by controlling the ranges and ratios of aluminum and magnesium and the ratio between the plated layer and the alloy layer to stably form a primary Al phase or an Al / Zn eutectoid phase.

[0023] FIG. 1 is a process flow chart showing a method for producing a highly corrosion-resistant plated steel material according to an embodiment of the present invention.

[0024] 1, the method for producing the highly corrosion-resistant plated steel material includes the steps of: immersing a base steel in a hot-dip alloy coating bath containing, by weight, 6% to 18% aluminum (Al), 3% to 6% magnesium (Mg), and the remainder being zinc (Zn) and other unavoidable impurities (S110); withdrawing the immersed base steel from the hot-dip alloy coating bath and forming a hot-dip alloy coating layer on the base steel (S120); and cooling the base steel with the hot-dip alloy coating layer formed thereon (S130), wherein the aluminum:magnesium content ratio in the hot-dip alloy coating bath is in the range of 2:1 to 6:1. This allows the formation of a coating layer with excellent corrosion resistance.

[0025] The hot-dip alloy plating bath can be maintained at a temperature in the range of 420°C to 500°C.

[0026] The hot dip alloy plating bath may be maintained at a temperature in the range of 20°C to 50°C above the melting point of the molten alloy.

[0027] The cooling step may have a cooling rate of 7°C / sec to 30°C / sec.

[0028] The cooling step may have a cooling rate of 10°C / sec to 15°C / sec.

[0029] The hot-dip alloy coating layer may include a coating base layer and an Fe—Al alloy layer, and the total thickness of the hot-dip alloy coating layer may be at least twice the thickness of the Fe—Al alloy layer.

[0030] The plating base layer may contain a primary Al phase (a single-phase structure of Al with Zn solid solution), an Al / Zn eutetoid phase, or both.

[0031] In the hot-dip alloy plating layer, the area fraction of the primary Al phase, the Al / Zn eutectoid phase, or both of them may be in the range of 20% to 60%.

[0032] The highly corrosion-resistant plated steel material produced by the above-described method for producing a highly corrosion-resistant plated steel material includes: a base iron; and a hot-dip alloy plating layer formed on the base iron, the hot-dip alloy plating layer containing, by weight, 6% to 18% aluminum (Al), 3% to 6% magnesium (Mg), and the balance zinc (Zn) and other unavoidable impurities; the hot-dip alloy plating layer includes a plating base layer and an Fe—Al alloy layer, and the total thickness of the hot-dip alloy plating layer may be at least twice the thickness of the Fe—Al alloy layer.

[0033] The plating base layer contains a primary Al phase, an Al / Zn eutectoid phase, or both, and the area fraction of the primary Al phase, the Al / Zn eutectoid phase, or both in the hot-dip alloy plating layer may be in the range of 20% to 60%.

[0034] The aluminum added to the hot-dip alloy plating bath is added to prevent oxidation of magnesium during plating. When the amount of magnesium added to the hot-dip alloy plating bath is 3% or more, the amount of aluminum added must be at least twice the amount of magnesium added to prevent oxidation of magnesium in the hot-dip alloy plating bath and reduce oxidation dross.

[0035] The aluminum:magnesium content ratio of the hot-dip alloy plating layer may be in the range of 2:1 to 6:1.

[0036] When 6% or more of aluminum is added to the hot-dip alloy coating bath, a primary Al phase or an Al / Zn eutectoid phase can be formed in the hot-dip alloy coating layer formed on the steel substrate during solidification after coating. The primary Al phase or Al / Zn eutectoid phase forms a structurally strong passive layer in a corrosive environment, improving corrosion resistance and providing crack resistance to the coating layer. Within the composition range of the present invention, a eutectic phase with a lamellar structure and high hardness is formed in most cases, and primary Al, which has excellent elongation properties, improves crack resistance.

[0037] However, in order for the primary Al phase or the Al / Zn eutectoid phase to form, the formation of an Fe-Al alloy layer between the steel substrate and the hot-dip alloy coating layer must be prevented or at least minimized. If aluminum is added to the hot-dip alloy coating bath in an amount exceeding 18%, the Fe-Al alloy layer grows excessively, resulting in an insufficient aluminum content for the formation of the primary Al phase or the Al / Zn eutectoid phase, and as a result, the amount of the primary Al phase or the Al / Zn eutectoid phase formed in the hot-dip alloy coating layer is rapidly reduced.

[0038] Furthermore, if more than 18% aluminum is added to the molten alloy plating bath, the melting temperature increases regardless of the amount of magnesium added, and the diffusion rate of the alloy layer increases rapidly in the plating layer formation step, so that the primary Al and / or Al / Zn eutectoid phase is not formed.

[0039] On the other hand, if aluminum is added to the hot-dip alloy plating bath in an amount less than 6%, the aluminum content will be insufficient, and the primary Al phase or the Al / Zn eutectoid phase may not be sufficiently formed.

[0040] If the magnesium content is less than 3% by weight, it may only contribute slightly to corrosion resistance, whereas if the magnesium content exceeds 5% by weight, it may cause deterioration in the quality of the steel material due to magnesium oxide dross.

[0041] To prevent the primary Al phase or the Al / Zn eutectoid phase from decreasing, the aluminum:magnesium content ratio is controlled to a range of 2:1 to 6:1. At this content ratio, the primary Al phase or the Al / Zn eutectoid phase can be sufficiently formed. The magnesium acts to prevent the diffusion of elements required for the formation of the Fe-Al alloy layer, suppressing the growth of the Fe-Al alloy layer thickness and, as a result, facilitating the formation of the primary Al phase or the Al / Zn eutectoid phase.

[0042] The hot-dip alloy coating layer can include a coating base layer and an Fe-Al alloy layer. The coating base layer is formed on the base steel by the components of the hot-dip alloy coating bath and refers to a layer having a composition similar to the composition range of the hot-dip alloy coating bath. The Fe-Al alloy layer is formed by alloying the iron contained in the base steel with the aluminum contained in the hot-dip alloy coating bath, and refers to a layer formed mainly at the interface between the base steel and the hot-dip alloy coating layer. In order to form the highly corrosion-resistant coated steel material of the present invention, it is preferable to prevent or suppress the formation of the Fe-Al alloy layer as much as possible.

[0043] The formation of such an Fe—Al alloy layer can be affected by the temperature of the hot-dip alloy plating bath, which can be maintained at a temperature in the range of 420°C to 500°C, or at a temperature 20°C to 50°C above the melting point of the molten alloy.

[0044] Since the formation of the Fe-Al alloy layer also occurs in the cooling step after the formation of the hot-dip alloy coating layer, a cooling rate that minimizes the formation of the Fe-Al alloy layer is required. Accordingly, the cooling step may have a cooling rate of 7°C / s to 30°C / s. Preferably, a cooling rate of 10°C / s to 15°C / s allows for the production of a coated steel material with excellent corrosion resistance and coating workability. If the cooling rate is less than 7°C / s, the Fe-Al alloy layer continues to grow during solidification, making it difficult to form a primary Al phase or an Al / Zn eutectoid phase. If the cooling rate exceeds 30°C / s, the appearance of the coating surface may solidify unevenly, resulting in a deterioration in the surface quality of the steel material. A lower cooling rate promotes the formation of the primary Al phase, while a higher cooling rate promotes the formation of the Al / Zn eutectoid phase.

[0045] Furthermore, to facilitate the formation of the primary Al phase or the Al / Zn eutectoid phase, it is necessary to control the thickness of the alloy layer in the entire plating layer. The total thickness of the hot-dip alloy plating layer must be at least twice the thickness of the Fe-Al alloy layer, and may be, for example, in the range of 2 to 20 times. If the total thickness of the hot-dip alloy plating layer is less than twice the thickness of the Fe-Al alloy layer, the fraction of the primary Al phase or the Al / Zn eutectoid phase in the hot-dip alloy plating layer will rapidly decrease, which will simultaneously reduce the corrosion resistance and the workability of the plating layer.

[0046] In a cross section (e.g., a longitudinal section) of the hot-dip alloy coating layer, the area fraction of the primary Al phase, the Al / Zn eutectoid phase, or both may be in the range of 20% to 60%. The remaining fractions are MgZn2 phase, Mg2Zn 11The primary Al phase may include a binary eutectic phase containing two elements selected from zinc, aluminum, and magnesium, or an Al / Zn / Mg ternary eutectic phase containing three elements, such as a primary Al phase. The area fraction may range from 40% to 80%. This area fraction may exclude the Fe-Al alloy phase. The area fraction refers to the area ratio determined by an image analyzer using a microstructure photograph of the steel material. If the area fraction of the primary Al phase, the Al / Zn eutectoid phase, or both is less than 20%, corrosion resistance will not be improved. If the area fraction of the primary Al phase, the Al / Zn eutectoid phase, or both is more than 60%, an excessive amount of MgZn2 phase, which has brittle properties, will be formed around the primary Al phase, which may cause cracks in the coating layer.

[0047] Experimental Example

[0048] Below, preferred experimental examples are presented to aid in understanding the present invention. However, the following experimental examples are merely provided to aid in understanding the present invention, and the present invention is not limited to these experimental examples. Contents not described here can be fully inferred by those skilled in the art, and therefore, explanations thereof will be omitted.

[0049] A 1.2 mm cold-rolled steel sheet is prepared as the base steel. The base steel contains 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) and impurities unavoidably contained in the steelmaking process. However, the composition and contents of the base steel are merely examples, and the technical concept of the present invention is not limited thereto.

[0050] The raw iron is immersed in an alkaline solution at 50°C for about 30 minutes, and then washed with water to remove foreign matter and oil from the surface.The raw iron is then annealed at a temperature of 680°C to 850°C in a reducing atmosphere consisting of nitrogen gas containing 7% hydrogen gas.

[0051] The annealed base steel was cooled to a temperature within ±20°C of the coating bath temperature, and then immersed in a 420°C to 500°C hot-dip alloy coating bath for 1 to 5 seconds. The total thickness of the hot-dip alloy coating layer was then adjusted to approximately 20 μm by nitrogen wiping. The coated base steel was then cooled to produce coated steel.

[0052] The corrosion resistance of the plated steel material was evaluated by a salt spray test using a 5% NaCl solution at 35°C to evaluate the time it took for red rust to appear.

[0053] Table 1 shows the compositions of the hot-dip alloy plating baths used to produce plated steel materials in the examples and comparative examples of the present invention.

[0054] [Table 1]

[0055] Referring to Table 1, the hot-dip alloy plating bath of the example contains, in weight percent, 6% to 18% aluminum (Al), 3% to 6% magnesium (Mg), and the remainder zinc (Zn) and other unavoidable impurities, with the aluminum:magnesium content ratio satisfying the range of 2:1 to 6:1.

[0056] Comparative Example 1 differs in that the aluminum content is lower than the lower limit proposed by the present invention and does not contain magnesium. Comparative Example 2 differs in that the aluminum content is lower than the lower limit proposed by the present invention and does not satisfy the aluminum:magnesium content ratio. Comparative Example 3 differs in that the aluminum content and magnesium content are each lower than the lower limits proposed by the present invention. Comparative Example 4 differs in that the aluminum content is higher than the upper limit proposed by the present invention and the magnesium content is lower than the lower limit proposed by the present invention. Comparative Example 5 differs in that the magnesium content is lower than the lower limit proposed by the present invention and does not satisfy the aluminum:magnesium content ratio. Comparative Example 6 differs in that the cooling rate is lower than the lower limit proposed by the present invention.

[0057] Here, the overall composition of the hot-dip alloy coating layer of the plated steel material is shown to be the same as or substantially similar to the composition of the hot-dip alloy coating bath. Therefore, the composition of the hot-dip alloy coating bath in Table 1 can be considered as the composition of the overall coating layer of the plated steel material.

[0058] Table 2 shows the properties and corrosion resistance of the hot-dip alloy plating layers of the plated steel materials of the examples of the present invention and the comparative examples.

[0059] [Table 2]

[0060] The evaluation of the time to red rust formation in Table 2 is as follows: ⊚: 2400 hours or more, ○: 1800 hours or more but less than 2400 hours, △: 800 hours or more but less than 1800 hours, ×: less than 600 hours.

[0061] Referring to Table 2, it can be seen that in the examples, the area fraction of the primary Al phase, the Al / Zn eutectoid phase, or both is 20% or more, which satisfies the range of 20% to 60% proposed by the present invention. In the examples, the thickness of the Fe-Al alloy layer is 7 μm or less, and the total thickness of the hot-dip alloy plating layer is more than twice the thickness of the Fe-Al alloy layer. In the examples, the time for red rust generation is 1,800 hours or more, which indicates that the examples have excellent corrosion resistance.

[0062] In Comparative Example 1, the aluminum content was low, so the primary Al phase or Al / Zn eutectoid phase was not formed, and the thickness of the Fe-Al alloy layer was small. However, the time for red rust to appear was less than 600 hours, so the corrosion resistance was evaluated as poor.

[0063] In Comparative Example 2, due to the low aluminum content, the primary Al phase or Al / Zn eutectoid phase was hardly formed, and the thickness and thickness ratio of the Fe-Al alloy layer were small due to the low aluminum content. However, since the time for red rust to occur was between 800 hours and less than 1800 hours, the corrosion resistance was evaluated as poor.

[0064] In Comparative Example 3, due to the low aluminum content, a small proportion of primary Al phase or Al / Zn eutectoid phase was formed, and the thickness and thickness ratio of the Fe-Al alloy layer were small due to the low aluminum content. However, since the time for red rust to occur was between 800 hours and less than 1800 hours, the corrosion resistance was evaluated as poor.

[0065] In Comparative Example 4, the aluminum content was high and the magnesium content was low, so that a primary Al phase or an Al / Zn eutectoid phase was not formed, and instead a thick Fe-Al alloy layer was formed. The time for red rust to appear was 800 hours or more but less than 1800 hours, and therefore the corrosion resistance was evaluated as poor.

[0066] In Comparative Example 5, the low magnesium content prevented the formation of a sufficient amount of primary Al phase or Al / Zn eutectoid phase, and instead a thick Fe-Al alloy layer was formed, and the time for red rust to occur was 800 hours or more but less than 1800 hours, so the corrosion resistance was evaluated as poor.

[0067] In Comparative Example 6, the aluminum and magnesium contents were at appropriate levels, but the cooling rate was low, so a primary Al phase or Al / Zn eutectoid phase could not be formed in sufficient amounts. Instead, a thick Fe-Al alloy layer was formed, and the time for red rust to occur was 800 hours or more but less than 1800 hours, so the corrosion resistance was evaluated as poor.

[0068] Therefore, in order for the primary Al phase or Al / Zn eutectoid phase to be formed in the hot-dip alloy layer, the ratio of the total thickness of the hot-dip alloy layer to the thickness of the Fe-Al alloy layer must be 2:1 or more, i.e., the total thickness of the hot-dip alloy layer must be at least twice as thick as the thickness of the Fe-Al alloy layer. Furthermore, it is preferable that the area fraction of the primary Al phase or Al / Zn eutectoid phase present in the hot-dip alloy layer is in the range of 20% to 60% based on the cross section of the hot-dip alloy layer.

[0069] FIG. 2 is a scanning electron microscope photograph showing the microstructure of a highly corrosion-resistant plated steel material according to an embodiment of the present invention.

[0070] FIG. 2(a) shows Comparative Example 4, in which the aluminum content was higher than the upper limit suggested by the present invention and the magnesium content was lower than the lower limit suggested by the present invention, resulting in a thick Fe-Al alloy layer of about 12 μm formed on the base steel.

[0071] FIG. 2(b) shows Example 2, in which a thin Fe—Al alloy layer was formed on the base steel with a thickness of about 1.5 μm, and the primary Al phase was formed at a fraction of about 26%.

[0072] (c) in Figure 2 shows Example 4, in which a thin Fe-Al alloy layer with a thickness of about 4 μm was formed on the base steel, and the primary Al phase and Al / Zn eutectoid phase were formed at a total fraction of about 30%.

[0073] As described above, it is clear that in the examples, the formation of the Fe-Al alloy layer is suppressed as much as possible, and the primary Al phase and Al / Zn eutectoid phase are sufficiently formed, thereby improving corrosion resistance.

[0074] It will be apparent to those skilled in the art to which the technical idea of ​​the present invention pertains that the technical idea of ​​the present invention described above is not limited to the above-described embodiments and the accompanying drawings, and that various substitutions, modifications and changes are possible within the scope of the technical idea of ​​the present invention. [Industrial Applicability]

[0075] According to one embodiment of the present invention as described above, a highly corrosion-resistant plated steel material can be provided that provides excellent corrosion resistance by generating a primary Al phase or an Al / Zn eutectoid phase and suppressing the formation of an Fe-Al alloy layer.

Claims

1. Immersing the base steel in a hot-dip alloy plating bath containing, by weight, 6% to 18% aluminum (Al), 3% to 6% magnesium (Mg), and the balance zinc (Zn) and other inevitable impurities; withdrawing the immersed base steel from the hot-dip alloy coating bath to form a hot-dip alloy coating layer on the base steel; and cooling the base steel on which the hot-dip alloy plating layer is formed, The aluminum:magnesium content ratio in the hot-dip alloy plating bath is in the range of 2:1 to 6:

1.

2. 2. The method for producing a highly corrosion-resistant plated steel material according to claim 1, wherein the hot-dip alloy plating bath is maintained at a temperature in the range of 420°C to 500°C.

3. 2. The method for producing a highly corrosion-resistant plated steel product according to claim 1, wherein the hot-dip alloy plating bath is maintained at a temperature increased by 20°C to 50°C above the melting point of the molten alloy.

4. The method for producing a highly corrosion-resistant plated steel material according to claim 1, wherein the cooling step has a cooling rate of 7°C / sec to 30°C / sec.

5. The method for producing a highly corrosion-resistant plated steel material according to claim 1, wherein the cooling step has a cooling rate of 10°C / sec to 15°C / sec.

6. the hot-dip alloy plating layer includes a plating base layer and an Fe—Al alloy layer, 2. The method for producing a highly corrosion-resistant plated steel material according to claim 1, wherein the total thickness of the hot-dip alloy plating layer is at least twice the thickness of the Fe—Al alloy layer.

7. The method for producing a highly corrosion-resistant plated steel material according to claim 6 , wherein the plating base layer contains a primary Al phase, an Al / Zn eutectoid phase, or both of them.

8. 8. The method for producing a highly corrosion-resistant plated steel material according to claim 7, wherein, in the hot-dip alloy plating layer, an area fraction of the primary Al phase, the Al / Zn eutectoid phase, or both of them is in a range of 20% to 60%.

9. With bare iron, a hot-dip alloy plating layer formed on the base steel, the hot-dip alloy plating layer containing, by weight, 6% to 18% aluminum (Al), 3% to 6% magnesium (Mg), and the balance zinc (Zn) and other inevitable impurities; the hot-dip alloy plating layer includes a plating base layer and an Fe—Al alloy layer, the plating base layer contains a primary Al phase, an Al / Zn eutectoid phase, or both of them; In the hot-dip alloy plating layer, the area fraction of the primary Al phase, the Al / Zn eutectoid phase, or both of them is in the range of 20% to 60%.

10. 10. The highly corrosion-resistant plated steel material according to claim 9, wherein the hot-dip alloy plating layer includes a plating base layer and an Fe—Al alloy layer, and a total thickness of the hot-dip alloy plating layer is at least twice the thickness of the Fe—Al alloy layer.

11. 10. The highly corrosion-resistant plated steel material according to claim 9, wherein the aluminum:magnesium content ratio of the hot-dip alloy plating layer is in the range of 2:1 to 6:1.

Images