Plated steel sheet and manufacturing method thereof

Abstract

The present invention provides a method for manufacturing a plated steel sheet, the method comprising the steps of: preparing a plating bath including a plating solution containing 10 wt % to 15 wt % of aluminum (Al), 4 wt % to 6.5 wt % of magnesium (Mg), and the balance of zinc (Zn) and other inevitable impurities; annealing a base steel; immersing the base steel after annealing in the plating bath; adjusting the amount of the plating solution on the base steel after immersion by using an air knife; and cooling the base steel in which the amount of the plating solution has been adjusted.

Description

Galvanized steel sheet and manufacturing method thereof

[0001] The present invention relates to a plated steel sheet having excellent crack resistance and corrosion resistance and a method for manufacturing the same.

[0002] Galvanized steel sheet has excellent sacrificial corrosion resistance. When exposed to a corrosive environment, the low-potential zinc preemptively dissolves, preventing corrosion of the steel. Due to these excellent corrosion properties, galvanized steel sheet is used in home appliances, building materials, and automobiles.

[0003] However, as industry becomes more advanced, resource depletion becomes more severe, and environmental regulations emerge, the need for the development of steel with improved corrosion resistance is increasing.

[0004] To improve these problems, research has been conducted since the early 2000s on high-corrosion-resistant galvanized steel sheets that improve the corrosion resistance of steel by adding elements such as aluminum and magnesium to the zinc plating bath.

[0005] However, zinc-aluminum-magnesium coated steel sheets had the problem of inferior workability compared to galvanized steel sheets.

[0006] Zinc-aluminum-magnesium plated steel forms hard intermetallic compounds, which causes cracks to form within the plated layer during processing.

[0007] This causes damage to the appearance during processing and causes moisture to seep through cracks, promoting corrosion.

[0008] The present invention is intended to solve various problems including the above-described problems, and according to one embodiment of the present invention, a plated steel sheet having excellent crack resistance and corrosion resistance and a method for manufacturing the same can be provided.

[0009] However, these tasks are exemplary and the scope of the present invention is not limited thereby.

[0010] According to one aspect of the present invention, a method for manufacturing a plated steel sheet is provided, comprising: a step of preparing a plating bath including a plating solution containing 10 wt% or more and 15 wt% or less of aluminum (Al), 4 wt% or more and 6.5 wt% or less of magnesium (Mg), the remainder zinc (Zn), and other unavoidable impurities; a step of annealing a base iron; a step of immersing the base iron after the annealing in the plating bath; a step of adjusting the amount of the plating solution on the base iron after the immersion using an air knife; and a step of cooling the base iron in which the amount of the plating solution has been adjusted.

[0011] According to one aspect of the present invention, a plated steel sheet is provided, in which the area ratio of an aluminum (Al) single phase to a MgZn2 phase on a cross-section of a plated layer is 0.1 or more and less than 0.5.

[0012] According to one embodiment of the present invention, as described above, a plated steel sheet with excellent crack resistance and corrosion resistance and a method for manufacturing the same can be provided. Of course, the scope of the present invention is not limited by these effects.

[0013] Figure 1 is a flowchart showing a method for manufacturing a plated steel sheet according to the present invention.

[0014] FIG. 2 is a drawing showing a vertical cross-section of a plated steel sheet according to one embodiment of the present invention.

[0015] Figure 3 is a drawing showing a vertical cross-section of a plated steel sheet according to a comparative example of the present invention.

[0016] Figure 4 is a drawing showing a vertical cross-section of a plated steel sheet according to a comparative example of the present invention.

[0017] In the step of preparing a plating bath, the contents of magnesium (Mg) and aluminum (Al) contained in the plating solution can satisfy the following equation 1.

[0018] <Formula 1>

[0019] 1.5*[Mg] ≤ [Al] ≤ 3.5*[Mg]

[0020] (Here, [X] is the content of X (wt%) based on the total weight of the plating solution)

[0021] At the stage of preparing the plating bath,

[0022] The content of magnesium (Mg) and aluminum (Al) contained in the above plating solution can satisfy the following equation 2.

[0023] 0.2 < {Mg} / {Al} ≤ 0.5

[0024] (Here, {X} is the content of X (at%) based on the total number of atoms in the plating solution)

[0025] In the above cooling step, the average cooling rate from the aluminum (Al) primary phase precipitation start temperature of the plating solution to the MgZn2 phase precipitation completion temperature may be 5 ℃ / s or more and 27 ℃ / s or less.

[0026] The step of annealing the above-mentioned steel may be performed by annealing the above-mentioned steel at a temperature of 680°C or higher and 850°C or lower.

[0027] In the step of immersing the base steel after annealing in the plating bath, the temperature of the plating bath may be 440°C or higher and 530°C or lower.

[0028] In the step of immersing the base iron after annealing in the plating bath, the difference between the temperature of the base iron after annealing and the temperature of the plating solution in the plating bath may be 30°C or less.

[0029] The average size based on the major axis of the above aluminum (Al) single phase may be 0.5 ㎛ or more and 30 ㎛ or less.

[0030] On the cross-section of the above plating layer, the aluminum (Al) single phase may have a shape in which at least a portion is surrounded by the MgZn2 phase.

[0031] Hereinafter, the present invention will be described in detail. When describing the present invention, if it is determined that a detailed description of a related known technology or configuration may unnecessarily obscure the gist of the present invention, such detailed description will be omitted.

[0032] In the examples below, the terms first, second, etc. are not used in a limiting sense, but are used for the purpose of distinguishing one component from another.

[0033] In the examples below, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0034] In the following examples, when various components such as layers, films, regions, and plates are said to be “on” other components, this includes not only cases where they are “directly on” other components, but also cases where other components are interposed between them.

[0035] For convenience of explanation, the sizes of components in the drawings may be exaggerated or reduced. For example, the sizes and thicknesses of each component shown in the drawings are arbitrarily shown for convenience of explanation, and the present invention is not necessarily limited to what is shown.

[0036] In the following examples, terms such as “include” or “have” mean that a feature or component described in the specification is present, and do not preclude the possibility that one or more other features or components may be added.

[0037] In this specification, “A and / or B” refers to the case where it is A, or B, or both A and B. In addition, in this specification, “at least one of A and B” refers to the case where it is A, or B, or both A and B.

[0038] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0039] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0040] Figure 1 is a flowchart showing a method for manufacturing a plated steel sheet according to the present invention.

[0041] Referring to FIG. 1, a method for manufacturing a plated steel sheet according to the present invention may include a step of annealing a base steel (S100), a step of immersing the base steel in a plating bath (S200), a step of controlling a plating amount using an air knife (S300), and a cooling step (S400).

[0042] In the step of annealing the base steel (S100), the base steel can be annealed so that the plating solution is well absorbed on the surface of the base steel.

[0043] In the step of annealing the steel (S100), the steel can be annealed at a temperature of 680°C or higher and 850°C or lower.

[0044] After the step of annealing the steel base (S100), the step of immersing the steel base in a plating bath (S200) can be performed.

[0045] In the step of immersing the base iron in the plating bath (S200), a plating bath containing a plating solution in which the base iron is immersed can be prepared.

[0046] The plating solution may contain, based on the total weight of the plating solution, 4 wt% or more and 6.5 wt% or less of magnesium (Mg), 10 wt% or more and 15 wt% or less of aluminum (Al), the remainder zinc (Zn), and other unavoidable impurities.

[0047] If magnesium (Mg) is less than 4 wt%, the corrosion resistance of the final product, the plated steel sheet, may not be sufficient. If magnesium (Mg) is more than 6.5 wt%, the MgZn2 phase may become coarse, resulting in poor crack resistance.

[0048] If the aluminum (Al) content is less than 10 wt%, magnesium (Mg) oxidation is accelerated, and oxides float to the surface of the plating bath, which may prevent the process from proceeding. If the aluminum (Al) content exceeds 15 wt%, problems such as accelerated erosion of the potrol and difficulty in managing the plating bath dross may occur. In addition, excessive growth of a discontinuous interfacial alloy layer between the steel and the plating layer may occur, resulting in poor adhesion of the plating layer.

[0049] Aluminum (Al) and magnesium (Mg) contained in the plating solution can satisfy the following equations 1 and 2.

[0050] <Formula 1>

[0051] 1.5*[Mg] ≤ [Al] ≤ 3.5*[Mg]

[0052] (Here, [X] is the content of X (wt%) based on the total weight of the plating solution)

[0053] If the aluminum (Al) content (wt%) is less than 1.5 times the magnesium (Mg) content (wt%), oxidation of magnesium (Mg) is promoted, and oxides float to the surface of the plating bath, making it impossible to proceed with the process.

[0054] If the aluminum (Al) content (wt%) exceeds 3.5 times the magnesium (Mg) content (wt%), problems such as accelerated erosion of the plating roll and difficulty in managing the plating bath dross may occur. In addition, problems such as excessive growth of a discontinuous interfacial alloy layer between the steel and the plating layer may occur, resulting in poor adhesion of the plating layer.

[0055] <Formula 2>

[0056] 0.2 < {Mg} / {Al} ≤ 0.5

[0057] (Here, {X} is the content of X (at%) based on the total number of atoms in the plating solution)

[0058] If the ratio of the magnesium (Mg) content (at%) to the aluminum (Al) content (at%) is less than 0.2, excessive growth of the interface alloy layer may occur, resulting in reduced corrosion resistance and poor plating surface quality.

[0059] If the ratio of the content (at%) of magnesium (Mg) to the content (at%) of aluminum (Al) exceeds 0.5, the MgZn2 phase becomes coarse, resulting in poor crack resistance and accelerated oxidation of magnesium (Mg), which may cause problems such as deterioration in operability.

[0060] In one embodiment, the temperature of the plating solution may be 440°C or higher and 530°C or lower.

[0061] In the step of annealing the steel base (S100), the steel base is annealed at a temperature of 680°C or higher and 850°C or lower, but the temperature of the steel base may drop during the process of moving the annealed steel base to the plating bath.

[0062] In the step of immersing the base iron in the plating bath (S200), the difference between the temperature of the base iron after annealing and the temperature of the plating solution in the plating bath may be 30°C or less.

[0063] After immersing the steel in a plating bath, a step (S300) of adjusting the plating amount using an air knife can be performed.

[0064] Since it is not desirable for the plating layer to be excessively thick, the amount of plating solution (plating amount) on the base iron can be adjusted using an air knife.

[0065] At this time, the plating amount is 30 g / m on one side of the steel sheet. 2 More than 500 g / m 2 It could be as follows:

[0066] After that, a step (S400) of cooling the base iron with adjusted plating amount can be performed.

[0067] In the cooling step (S400), the average cooling rate from the aluminum (Al) primary phase precipitation start temperature to the MgZn2 phase precipitation completion temperature may be 5 ℃ / s or more and 27 ℃ / s or less.

[0068] If the average cooling rate is less than 5 ℃ / s, the aluminum (Al) phase may grow coarsely, which may result in poor corrosion resistance, and if the average cooling rate exceeds 27 ℃ / s, the size of the aluminum (Al) single phase within the MgZn2 phase may become fine during cooling, which may result in poor crack resistance.

[0069] In one embodiment, the average cooling rate from the aluminum (Al) primary phase precipitation initiation temperature to the MgZn2 phase precipitation completion temperature may be 7°C / s or more and 20°C / s or less.

[0070] In the present invention, the aluminum (Al) single phase within the MgZn2 phase may include not only a case where the aluminum (Al) single phase is entirely contained within the MgZn2 phase, but also a case where at least a portion of the aluminum (Al) single phase is contained within the MgZn2 phase.

[0071] In addition, in the present invention, the aluminum (Al) single phase is a single phase in which aluminum (Al) is the main component, and may include not only a single phase containing only aluminum (Al), but also a phase in which aluminum (Al) is the main component and contains 20 wt% to 60 wt% of zinc and other impurities.

[0072] galvanized steel plate

[0073] A plated steel sheet according to one embodiment of the present invention can be manufactured by the above-described plated steel sheet manufacturing method.

[0074] When a cross-section of a plated steel sheet is taken that is approximately perpendicular to the surface of the steel sheet, the aluminum (Al) single phase may have a shape in which at least a portion of the plated layer is surrounded by a MgZn2 phase.

[0075] In addition, the area ratio of the aluminum (Al) single phase to the MgZn2 phase on the cross-section of the plating layer may be 0.1 or more and less than 0.5. In addition, the average size based on the long axis of the aluminum (Al) single phase may be 0.5 ㎛ or more and 30 ㎛ or less.

[0076] In the case of having the above-mentioned area ratio and average size of the aluminum (Al) single phase, due to the difference in hardness between the MgZn2 phase and the aluminum (Al) single phase, when a crack propagates in the MgZn2 phase with relatively high hardness, the aluminum (Al) single phase with relatively low hardness can absorb the impact and prevent the crack from propagating.

[0077] Additionally, if the area ratio of the aluminum (Al) single phase to the MgZn2 phase exceeds 0.5, corrosion resistance may be deteriorated.

[0078] Hereinafter, the structure and operation of the present invention will be described in more detail through preferred embodiments of the present invention. However, these are presented as preferred examples of the present invention and should not be construed as limiting the present invention in any way.

[0079] Experimental example

[0080] Below, the present invention will be described in more detail through experimental examples. However, the following experimental examples are intended to further illustrate the present invention, and the scope of the present invention is not limited by these examples. Those skilled in the art may appropriately modify or alter the following experimental examples within the scope of the present invention.

[0081] Plating solution composition Plating solution temperature (℃) Average cooling rate (℃ / s) {Mg} / {Al} Al single phase area ratio Al single phase size (㎛) Mg (wt%) Al (wt%)Example 1412460120.370.25.12Example 2414.5470200.310.241.13Example 3414.546550.310.2729Example 4512460170.460.282.79Example 5514.5460130.380.344.2Example 651446080.40.2419Example 75.514.546560.420.1819.8Example 8615480110.440.256.3Example 961448 0100.480.276Comparative Example 1412460290.370.2060.45Comparative Example 2414.546530.310.25632Comparative Example 34.525480150.20.410.2Comparative Example 451246030.460.23731.2Comparative Example 55.514.5465300.420.1830.47Comparative Example 66.51448570.520.238Comparative Example 7712485110.650.263.5Comparative Example 8612480150.560.232.4

[0082] Table 1 above is a table showing the magnesium (Mg) and aluminum (Al) contents (wt%) contained in the plating solutions of examples and comparative examples, the plating solution temperature, the average cooling rate from the aluminum (Al) primary phase precipitation start temperature in the cooling step to the MgZn2 phase precipitation completion temperature, the ratio of the magnesium (Mg) content (at%) to the aluminum (Al) content (at%), the area ratio of the aluminum (Al) single phase to the MgZn2 phase, and the average size based on the long axis of the aluminum (Al) single phase.

[0083] Example 1

[0084] A plating solution containing magnesium (Mg) and aluminum (Al) contents (wt%), the remainder zinc (Zn), and other unavoidable impurities according to Table 1 above was prepared.

[0085] At this time, the temperature of the plating solution was 460 ℃ and the ratio of the magnesium (Mg) content (at%) to the aluminum (Al) content (at%) was 0.37.

[0086] The average cooling rate from the initiation temperature of aluminum (Al) primary phase precipitation to the completion temperature of MgZn2 phase precipitation in the cooling stage was 12 ℃ / s.

[0087] As a result, the area ratio of the aluminum (Al) single phase to the MgZn2 phase on the cross-section of the plating layer of the plated steel plate was 0.2, and the average size based on the long axis of the aluminum (Al) single phase was 5.12 ㎛.

[0088] Example 2

[0089] A plating solution containing magnesium (Mg) and aluminum (Al) contents (wt%) according to Table 1 above, the remainder zinc (Zn), and other unavoidable impurities was used, and the temperature of the plating solution was 470°C, the ratio of the magnesium (Mg) content (at%) to the aluminum (Al) content (at%) was 0.31, and the average cooling rate from the aluminum (Al) primary phase precipitation start temperature to the MgZn2 phase precipitation completion temperature in the cooling step was 20°C / s, except that the plating solution was manufactured in the same manner as in Example 1.

[0090] As a result, the area ratio of the aluminum (Al) single phase to the MgZn2 phase on the cross-section of the plating layer of the plated steel plate was 0.24, and the average size based on the long axis of the aluminum (Al) single phase was 1.13 ㎛.

[0091] Example 3

[0092] A plating solution containing magnesium (Mg) and aluminum (Al) contents (wt%) according to Table 1 above, the remainder zinc (Zn), and other unavoidable impurities was used, and the temperature of the plating solution was 465°C, the ratio of the magnesium (Mg) content (at%) to the aluminum (Al) content (at%) was 0.31, and the average cooling rate from the aluminum (Al) primary phase precipitation start temperature to the MgZn2 phase precipitation completion temperature in the cooling step was 5°C / s, except that the plating solution was manufactured in the same manner as in Example 1.

[0093] As a result, the area ratio of the aluminum (Al) single phase to the MgZn2 phase on the cross-section of the plating layer of the plated steel plate was 0.27, and the average size based on the long axis of the aluminum (Al) single phase was 29 ㎛.

[0094] Example 4

[0095] A plating solution containing magnesium (Mg) and aluminum (Al) contents (wt%) according to Table 1 above, the remainder zinc (Zn), and other unavoidable impurities was used, and the temperature of the plating solution was 460°C, the ratio of the magnesium (Mg) content (at%) to the aluminum (Al) content (at%) was 0.46, and the average cooling rate from the aluminum (Al) primary phase precipitation start temperature to the MgZn2 phase precipitation completion temperature in the cooling step was 17°C / s, except that the plating solution was manufactured in the same manner as in Example 1.

[0096] As a result, the area ratio of the aluminum (Al) single phase to the MgZn2 phase on the cross-section of the plating layer of the plated steel plate was 0.28, and the average size based on the long axis of the aluminum (Al) single phase was 2.79 ㎛.

[0097] Example 5

[0098] A plating solution containing magnesium (Mg) and aluminum (Al) contents (wt%) according to Table 1 above, the remainder zinc (Zn), and other unavoidable impurities was used, and the temperature of the plating solution was 460°C, the ratio of the magnesium (Mg) content (at%) to the aluminum (Al) content (at%) was 0.38, and the average cooling rate from the aluminum (Al) primary phase precipitation start temperature to the MgZn2 phase precipitation completion temperature in the cooling step was 13°C / s, except that the plating solution was manufactured in the same manner as in Example 1.

[0099] As a result, the area ratio of the aluminum (Al) single phase to the MgZn2 phase on the cross-section of the plating layer of the plated steel plate was 0.34, and the average size based on the long axis of the aluminum (Al) single phase was 4.2 ㎛.

[0100] Example 6

[0101] A plating solution containing magnesium (Mg) and aluminum (Al) contents (wt%) according to Table 1 above, the remainder zinc (Zn), and other unavoidable impurities was used, and the temperature of the plating solution was 460°C, the ratio of the magnesium (Mg) content (at%) to the aluminum (Al) content (at%) was 0.4, and the average cooling rate from the aluminum (Al) primary phase precipitation start temperature to the MgZn2 phase precipitation completion temperature in the cooling step was 8°C / s, except that the plating solution was manufactured in the same manner as in Example 1.

[0102] As a result, the area ratio of the aluminum (Al) single phase to the MgZn2 phase on the cross-section of the plating layer of the plated steel plate was 0.24, and the average size based on the long axis of the aluminum (Al) single phase was 19 ㎛.

[0103] Example 7

[0104] A plating solution containing magnesium (Mg) and aluminum (Al) contents (wt%) according to Table 1 above, the remainder zinc (Zn), and other unavoidable impurities was used, and the temperature of the plating solution was 465°C, the ratio of the magnesium (Mg) content (at%) to the aluminum (Al) content (at%) was 0.42, and the average cooling rate from the aluminum (Al) primary phase precipitation start temperature to the MgZn2 phase precipitation completion temperature in the cooling step was 6°C / s, except that the plating solution was manufactured in the same manner as in Example 1.

[0105] As a result, the area ratio of the aluminum (Al) single phase to the MgZn2 phase on the cross-section of the plating layer of the plated steel plate was 0.181, and the average size based on the long axis of the aluminum (Al) single phase was 9.8 ㎛.

[0106] Example 8

[0107] A plating solution containing magnesium (Mg) and aluminum (Al) contents (wt%) according to Table 1 above, the remainder zinc (Zn), and other unavoidable impurities was used, and the temperature of the plating solution was 480°C, the ratio of the magnesium (Mg) content (at%) to the aluminum (Al) content (at%) was 0.44, and the average cooling rate from the aluminum (Al) primary phase precipitation start temperature to the MgZn2 phase precipitation completion temperature in the cooling step was 11°C / s, except that the plating solution was manufactured in the same manner as in Example 1.

[0108] As a result, the area ratio of the aluminum (Al) single phase to the MgZn2 phase on the cross-section of the plating layer of the plated steel plate was 0.25, and the average size based on the long axis of the aluminum (Al) single phase was 6.3 ㎛.

[0109] Example 9

[0110] A plating solution containing magnesium (Mg) and aluminum (Al) contents (wt%) according to Table 1 above, the remainder zinc (Zn), and other unavoidable impurities was used, and the temperature of the plating solution was 480°C, the ratio of the magnesium (Mg) content (at%) to the aluminum (Al) content (at%) was 0.48, and the average cooling rate from the aluminum (Al) primary phase precipitation start temperature to the MgZn2 phase precipitation completion temperature in the cooling step was 10°C / s, except that the plating solution was manufactured in the same manner as in Example 1.

[0111] As a result, the area ratio of the aluminum (Al) single phase to the MgZn2 phase on the cross-section of the plating layer of the plated steel plate was 0.27, and the average size based on the long axis of the aluminum (Al) single phase was 6 ㎛.

[0112] Comparative Example 1

[0113] A plating solution containing magnesium (Mg) and aluminum (Al) contents (wt%) according to Table 1 above, the remainder zinc (Zn), and other unavoidable impurities was used, and the temperature of the plating solution was 460°C, the ratio of the magnesium (Mg) content (at%) to the aluminum (Al) content (at%) was 0.37, and the average cooling rate from the aluminum (Al) primary phase precipitation start temperature to the MgZn2 phase precipitation completion temperature in the cooling step was 29°C / s, except that the plating solution was manufactured in the same manner as in Example 1.

[0114] As a result, the area ratio of the aluminum (Al) single phase to the MgZn2 phase on the cross-section of the plating layer of the plated steel plate was 0.206, and the average size based on the long axis of the aluminum (Al) single phase was 0.45 ㎛.

[0115] Comparative Example 2

[0116] A plating solution containing magnesium (Mg) and aluminum (Al) contents (wt%) according to Table 1 above, the remainder zinc (Zn), and other unavoidable impurities was used, and the temperature of the plating solution was 465°C, the ratio of the magnesium (Mg) content (at%) to the aluminum (Al) content (at%) was 0.31, and the average cooling rate from the aluminum (Al) primary phase precipitation start temperature to the MgZn2 phase precipitation completion temperature in the cooling step was 3°C / s, except that the plating solution was manufactured in the same manner as in Example 1.

[0117] As a result, the area ratio of the aluminum (Al) single phase to the MgZn2 phase on the cross-section of the plating layer of the plated steel plate was 0.256, and the average size based on the long axis of the aluminum (Al) single phase was 32 ㎛.

[0118] Comparative Example 3

[0119] A plating solution containing magnesium (Mg) and aluminum (Al) contents (wt%) according to Table 1 above, the remainder zinc (Zn), and other unavoidable impurities was used, and the temperature of the plating solution was 480°C, the ratio of the magnesium (Mg) content (at%) to the aluminum (Al) content (at%) was 0.2, and the average cooling rate from the aluminum (Al) primary phase precipitation start temperature to the MgZn2 phase precipitation completion temperature in the cooling step was 15°C / s, except that the plating solution was manufactured in the same manner as in Example 1.

[0120] As a result, the area ratio of the aluminum (Al) single phase to the MgZn2 phase on the cross-section of the plating layer of the plated steel plate was 0.4, and the average size based on the long axis of the aluminum (Al) single phase was 10.2 ㎛.

[0121] Comparative Example 4

[0122] A plating solution containing magnesium (Mg) and aluminum (Al) contents (wt%) according to Table 1 above, the remainder zinc (Zn), and other unavoidable impurities was used, and the temperature of the plating solution was 460°C, the ratio of the magnesium (Mg) content (at%) to the aluminum (Al) content (at%) was 0.46, and the average cooling rate from the aluminum (Al) primary phase precipitation start temperature to the MgZn2 phase precipitation completion temperature in the cooling step was 3°C / s, except that the plating solution was manufactured in the same manner as in Example 1.

[0123] As a result, the area ratio of the aluminum (Al) single phase to the MgZn2 phase on the cross-section of the plating layer of the plated steel plate was 0.237, and the average size based on the long axis of the aluminum (Al) single phase was 31.2 ㎛.

[0124] Comparative Example 5

[0125] A plating solution containing magnesium (Mg) and aluminum (Al) contents (wt%) according to Table 1 above, the remainder zinc (Zn), and other unavoidable impurities was used, and the temperature of the plating solution was 465°C, the ratio of the magnesium (Mg) content (at%) to the aluminum (Al) content (at%) was 0.42, and the average cooling rate from the aluminum (Al) primary phase precipitation start temperature to the MgZn2 phase precipitation completion temperature in the cooling step was 30°C / s, except that the plating solution was manufactured in the same manner as in Example 1.

[0126] As a result, the area ratio of the aluminum (Al) single phase to the MgZn2 phase on the cross-section of the plating layer of the plated steel plate was 0.183, and the average size based on the long axis of the aluminum (Al) single phase was 0.47 ㎛.

[0127] Comparative Example 6

[0128] A plating solution containing magnesium (Mg) and aluminum (Al) contents (wt%) according to Table 1 above, the remainder zinc (Zn), and other unavoidable impurities was used, and the temperature of the plating solution was 485°C, the ratio of the magnesium (Mg) content (at%) to the aluminum (Al) content (at%) was 0.52, and the average cooling rate from the aluminum (Al) primary phase precipitation start temperature to the MgZn2 phase precipitation completion temperature in the cooling step was 7°C / s, except that the plating solution was manufactured in the same manner as in Example 1.

[0129] As a result, the area ratio of the aluminum (Al) single phase to the MgZn2 phase on the cross-section of the plating layer of the plated steel plate was 0.23, and the average size based on the long axis of the aluminum (Al) single phase was 8 ㎛.

[0130] Comparative Example 7

[0131] A plating solution containing magnesium (Mg) and aluminum (Al) contents (wt%) according to Table 1 above, the remainder zinc (Zn), and other unavoidable impurities was used, and the temperature of the plating solution was 485°C, the ratio of the magnesium (Mg) content (at%) to the aluminum (Al) content (at%) was 0.65, and the average cooling rate from the aluminum (Al) primary phase precipitation start temperature to the MgZn2 phase precipitation completion temperature in the cooling step was 11°C / s, except that the plating solution was manufactured in the same manner as in Example 1.

[0132] As a result, the area ratio of the aluminum (Al) single phase to the MgZn2 phase on the cross-section of the plating layer of the plated steel plate was 0.26, and the average size based on the long axis of the aluminum (Al) single phase was 3.5 ㎛.

[0133] Comparative Example 8

[0134] A plating solution containing magnesium (Mg) and aluminum (Al) contents (wt%) according to Table 1 above, the remainder zinc (Zn), and other unavoidable impurities was used, and the temperature of the plating solution was 480°C, the ratio of the magnesium (Mg) content (at%) to the aluminum (Al) content (at%) was 0.56, and the average cooling rate from the aluminum (Al) primary phase precipitation start temperature to the MgZn2 phase precipitation completion temperature in the cooling step was 15°C / s, except that the plating solution was manufactured in the same manner as in Example 1.

[0135] As a result, the area ratio of the aluminum (Al) single phase to the MgZn2 phase on the cross-section of the plating layer of the plated steel plate was 0.23, and the average size based on the long axis of the aluminum (Al) single phase was 2.4 ㎛.

[0136] Sectional interface alloy layer crack area fraction Unplated generation dross adsorption corrosion resistance Example 1 ◎◎◎◎○ Example 2 ○◎◎○◎ Example 3 ○◎◎○◎ Example 4 ○◎◎◎◎ Example 5 ○◎○○◎ Example 6 ○◎○○◎ Example 7 ○◎○○◎ Example 8 ○○○○◎ Example 9 ○○○○◎ Comparative Example 1 ◎△◎○○ Comparative Example 2 ○○◎○△ Comparative Example 3 △◎△△△ Comparative Example 4 ○○◎◎△ Comparative Example 5 ○△○○◎ Comparative Example 6◎△△○◎ Comparative Example 7◎△△○◎ Comparative Example 8◎△○○◎

[0137] FIG. 2 is a drawing showing a vertical cross-section of a plated steel sheet according to one embodiment of the present invention, and FIGS. 3 and 4 are drawings showing a vertical cross-section of a plated steel sheet according to one comparative example of the present invention.

[0138] Specifically, FIG. 2 is a drawing showing a cross-section of Example 1, FIG. 3 is a drawing showing a cross-section of Comparative Example 1, and FIG. 4 is a drawing showing a cross-section of Comparative Example 3.

[0139] The meanings of ◎, ○, and △ in Table 2 are as shown in Tables 3 to 7 below.

[0140] Interfacial alloy layer◎Interfacial alloy layer is 1㎛ or more and less than 3㎛○Interfacial alloy layer is 3㎛ or more and less than 5㎛△Interfacial alloy layer is 5㎛ or more

[0141] Classification Crack Area Fraction◎ Crack area fraction of 30% or less when evaluating bending○ Crack area fraction of more than 30% and less than 50% when evaluating bending△ Crack area fraction of more than 50% when evaluating bending

[0142] Occurrence of unplated area◎None○Less than 4 unplated areas under 100mm△4 or more unplated areas under 100mm or 1 or more unplated areas over 100mm

[0143] Distinction Dross Adsorption◎No Dross Adsorption on the Surface of the Plating Layer○Less than 10 Dross Adsorptions on the Surface of the Plating Layer△More than 10 Dross Adsorptions on the Surface of the Plating Layer

[0144] Corrosion resistance ◎ After 1,500 hours of outdoor exposure, less than 5% of cross-section red rust occurs ○ After 1,500 hours of outdoor exposure, 5% or more but less than 10% of cross-section red rust occurs △ After 1,500 hours of outdoor exposure, 10% or more of cross-section red rust occurs

[0145] Referring to FIGS. 2 to 4 and Table 2, Examples 1 to 9 have excellent plating quality because the interfacial alloy layer is not excessively formed, the plating layer is well absorbed on the surface of the base iron, and the amount of unplated metal is small.

[0146] In addition, it exhibits excellent crack resistance due to a low crack area fraction even during bending evaluation.

[0147] The bending workability was evaluated by observing the bent portion after 3T bending with a Field Emission Scanning Electron microscope (FE-SEM) at 200x and 500x magnifications, and then averaging the area of ​​the bending crack. Five samples were collected from each location of the specimens manufactured under each condition and evaluated.

[0148] And since it has the element content and the content relationship of magnesium (Mg) and aluminum (Al) within the above-described numerical range, dross adsorption is minimal and corrosion resistance is excellent.

[0149] In particular, referring to FIG. 2, in the case of Example 1, a relatively light-shaded aluminum (Al) single phase is surrounded by a relatively dark-shaded MgZn2 phase, and exhibits an aluminum (Al) single phase size of an appropriate size.

[0150] On the other hand, Comparative Example 1 exhibited low crack resistance as the aluminum (Al) single phase size was small due to the cooling rate being too high, and the crack area fraction exceeded 50% during the bending evaluation, and Comparative Example 2 exhibited low crack resistance as the aluminum (Al) single phase size was too large due to the cooling rate being too low.

[0151] In particular, referring to FIG. 3, it can be confirmed that the size of the aluminum (Al) single phase in Comparative Example 1 is small.

[0152] In Comparative Example 3, the content (wt%) of aluminum (Al) was too high, so an excessive interfacial alloy layer was formed, resulting in non-plating, a lot of dross adsorption, and poor corrosion resistance.

[0153] In particular, referring to FIG. 4, it can be confirmed that in the case of Comparative Example 3, an excessively thick interfacial alloy layer was formed between the base steel and the plating layer.

[0154] Comparative Example 4, like Comparative Example 2, had a cooling rate that was too low, resulting in an aluminum (Al) single phase size that was too large and low corrosion resistance.

[0155] Comparative Example 5, like Comparative Example 1, exhibited low crack resistance as the cooling rate was too high and the aluminum (Al) single phase size was small, resulting in a crack area fraction exceeding 50% during bending evaluation.

[0156] In Comparative Example 6, the ratio of the magnesium (Mg) content (at%) to the aluminum (Al) content (at%) was too high, resulting in a high crack area fraction and non-plating.

[0157] Comparative Example 7 had a high magnesium (Mg) content (wt%), and the ratio of the magnesium (Mg) content (at%) to the aluminum (Al) content (at%) was too high, resulting in a high crack area fraction and non-plating.

[0158] In Comparative Example 8, the ratio of the magnesium (Mg) content (at%) to the aluminum (Al) content (at%) was too high, resulting in a high crack area fraction.

[0159] The embodiments of the present invention are merely illustrative, and those skilled in the art will understand that various modifications and equivalent alternative embodiments are possible. Therefore, the true scope of technical protection of the present invention should be determined by the technical spirit of the appended claims.

Claims

1. In the method for manufacturing a galvanized steel plate, A step of preparing a plating bath, which includes a plating solution containing 10 wt% or more and 15 wt% or less of aluminum (Al), 4 wt% or more and 6.5 wt% or less of magnesium (Mg), the remainder zinc (Zn), and other unavoidable impurities; Step of annealing the iron; A step of immersing the base iron after annealing in the above plating bath; A step of controlling the amount of plating solution on the above-mentioned steel after immersion using an air knife; and A step of cooling the above-mentioned steel having an adjusted amount of plating solution; A method for manufacturing a plated steel sheet, comprising:

2. In paragraph 1, In the step of preparing the above plating bath, A method for manufacturing a plated steel sheet, wherein the content of magnesium (Mg) and aluminum (Al) contained in the above plating solution satisfies the following formula 1. <Formula 1> 1.5*[Mg] ≤ [Al] ≤ 3.5*[Mg] (Here, [X] is the content of X (wt%) based on the total weight of the plating solution) 3. In paragraph 1, In the step of preparing the above plating bath, A method for manufacturing a plated steel sheet, wherein the content of magnesium (Mg) and aluminum (Al) contained in the above plating solution satisfies the following formula 2. 0.2 < {Mg} / {Al} ≤ 0.5 (Here, {X} is the content of X (at%) based on the total number of atoms in the plating solution) 4. In paragraph 1, A method for manufacturing a plated steel sheet, wherein the cooling step has an average cooling rate of 5 ℃ / s or more and 27 ℃ / s or less from the initial precipitation temperature of the aluminum (Al) phase of the plating solution to the completion temperature of the precipitation of the MgZn2 phase.

5. In paragraph 1, A method for manufacturing a plated steel sheet, wherein the step of annealing the above-mentioned base steel is to anneale the above-mentioned base steel at a temperature of 680°C or higher and 850°C or lower.

6. In paragraph 1, A method for manufacturing a plated steel sheet, wherein in the step of immersing the base steel after annealing in the above-mentioned plating bath, the temperature of the plating bath is 440°C or more and 530°C or less.

7. In paragraph 6, A method for manufacturing a plated steel sheet, wherein, in the step of immersing the base steel after annealing in the plating bath, the difference between the temperature of the base steel after annealing and the temperature of the plating solution in the plating bath is 30°C or less.

8. A plated steel sheet manufactured according to the plated steel sheet manufacturing method of paragraph 1, A plated steel sheet, wherein the area ratio of the aluminum (Al) single phase to the MgZn2 phase on the cross-section of the plated layer is 0.1 or more and less than 0.

5.

9. In paragraph 8, A plated steel sheet having an average size of 0.5 ㎛ or more and 30 ㎛ or less based on the major axis of the above aluminum (Al) single phase.

10. In paragraph 8, A plated steel sheet having a shape in which, on a cross-section of the above plating layer, the aluminum (Al) single phase is at least partially surrounded by a MgZn2 phase.

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