KR20140129529A - Hot-dip aluminium based alloy coated steel sheet with excellent sacrificial protection and method of maunfacturing the same - Google Patents

Abstract

Disclosed are a molten aluminum-based coated steel sheet with excellent sacrificial protection appropriate to be used for a vehicle, a construction material, or the like by ensuring excellent sacrificial protection and corrosion resistance through control of alloy constituent, and a method for manufacturing the same. According to the present invention, the molten aluminum-based coated steel sheet includes a base steel plate and an alloy coated layer coated on a surface of the base steel plate. The alloy coated layer includes 8.0-9.0 wt% of magnesium (Mg), 4.0- 5.0 wt% of silicon (Si), and the remainder consisting of aluminum (Al).

Description

TECHNICAL FIELD [0001] The present invention relates to a hot-dip galvanized steel sheet excellent in sacrificial corrosion resistance and a method of manufacturing the same,

The present invention relates to a molten aluminum-based plated steel sheet and a method of manufacturing the same, and more particularly, to a method of manufacturing a molten aluminum-based plated steel sheet which is excellent in sacrificial corrosion resistance, Aluminum-plated steel sheet and a manufacturing method thereof.

In the case of steel sheets used for automobiles and building materials, high-strength, high corrosion resistance and excellent surface quality are required, and therefore, molten aluminum-plated steel sheets are mainly used.

In the case of a general molten aluminum-plated steel sheet, a very dense aluminum oxide film is formed on the surface of the steel sheet in the atmosphere. Therefore, the protective coating effect due to the aluminum oxide coating is very excellent and the corrosion rate of the steel sheet is extremely low, which can contribute to the improvement of the corrosion resistance of the surface of the steel sheet.

However, since the plated layer does not act as a sacrificial anode due to the aluminum oxide film, there is a fatal problem in the cross-sectional corrosion which must provide sacrificial protection to the base steel plate unlike the surface corrosion, Much research is underway to improve this.

A related prior art document is Korean Patent Laid-Open Publication No. 10-2008-0023141 (published on Mar. 12, 2008), and a surface treated steel sheet is described in this document.

It is an object of the present invention to provide a molten aluminum plated steel sheet excellent in sacrificial corrosion resistance suitable for use in automobiles, building materials and the like by securing an excellent sacrificial corrosion property through control of components of a plating layer coated on a surface of a substrate layer.

Another object of the present invention is to provide an alloy coating layer which is formed by immersing a base steel sheet in an aluminum-based plating solution composed of an Al-Mg-Si ternary system having an optimized composition ratio and coating the base steel sheet with a coating amount of 50 to 100 g / To provide a method of manufacturing a molten aluminum-based plated steel sheet which can secure an excellent sacrificial corrosion resistance.

According to an aspect of the present invention, there is provided a molten aluminum-based plated steel sheet comprising a base steel sheet and an alloy coating layer coated on the surface of the base steel sheet, wherein the alloy coating layer comprises magnesium (Mg) : 8.0 to 9.0 wt%, silicon (Si): 4.0 to 5.0 wt%, and the balance aluminum (Al).

According to another aspect of the present invention, there is provided a method of manufacturing a molten aluminum-based plated steel sheet, the method including the steps of: (a) providing a steel sheet containing 8.0 to 9.0 wt% of magnesium, 4.0 to 5.0 wt% of silicon, Al), the base steel sheet being immersed in a plating bath containing the aluminum base plating solution; And (b) removing the base steel sheet from the plating bath to form an alloy coating layer on the surface of the base steel sheet so as to be coated with a plating adhesion amount of 50 to 100 g / m < 2 >.

The molten aluminum-based galvanized steel sheet according to the present invention and the method for producing the same provide a ternary alloy coating layer of Al-Mg-Si having an optimized composition ratio on the surface of a base steel sheet, It can have excellent corrosion resistance against corrosion.

In addition, since the molten aluminum-based plated steel sheet according to the present invention and the manufacturing method thereof use a ternary plating solution of Al-Mg-Si at an optimized composition ratio, the melting point becomes lower and the hot-dip coating operation becomes easier There is an advantage to be able to.

1 is a cross-sectional view schematically showing a molten aluminum-based plated steel sheet according to an embodiment of the present invention.
2 is a process flow chart schematically showing a method of manufacturing a molten aluminum-based plated steel sheet according to an embodiment of the present invention.

Advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described in detail below. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a molten aluminum plated steel sheet having excellent sacrificial corrosion resistance according to a preferred embodiment of the present invention and its manufacturing method will be described in detail with reference to the accompanying drawings.

1 is a cross-sectional view schematically showing a molten aluminum-based plated steel sheet according to an embodiment of the present invention.

Referring to FIG. 1, a molten aluminum-based plated steel sheet 100 according to an embodiment of the present invention includes a base steel sheet 110 and an alloy plating layer 120.

The base steel sheet 110 may be a hot rolled steel sheet manufactured by a process of reheating slabs, hot rolling, and cooling / winding. Alternatively, the base steel sheet 110 may be a cold rolled steel sheet produced by pickling, cold rolling and annealing the hot-rolled steel sheet. That is, the base steel sheet 110 can be used without limitation in any of hot-rolled steel sheets, cold-rolled steel sheets, and the like.

The alloy coating layer 120 is formed on the surface of the base steel sheet. The alloy coating layer 120 may be formed on only one side of the base steel sheet 110, but more preferably on both sides of the base steel sheet 110.

At this time, the alloy coating layer 120 includes aluminum (Al), magnesium (Mg), and silicon (Si). In this way, when the alloy coating layer 120 is formed only from a ternary system of Al-Mg-Si, excellent corrosion resistance against cross-section corrosion can be ensured by having a low cost of production and excellent saccharification resistance.

For this purpose, the alloy coating layer 120 is composed of 8.0 to 9.0 wt% of magnesium (Mg), 4.0 to 5.0 wt% of silicon (Si), and the balance aluminum (Al). Particularly, it has been confirmed through experiments that the alloy coating layer 120 is more preferably composed of 8.3 to 8.6 wt% of magnesium (Mg), 4.5 to 4.8 wt% of silicon (Si), and the balance of aluminum (Al).

Hereinafter, the role and content of each component contained in the molten aluminum-based alloy coating layer will be described.

Magnesium (Mg)

Magnesium (Mg) contributes to improving the corrosion resistance of the surface and improving the corrosion resistance of the exposed portion of the base steel sheet in the cross section.

Aluminum has the disadvantage that it is easily exposed at the exposed part of the base steel early because it can not serve as a sacrificial anode for iron (Fe) in most environments except for marine areas with many chloride ions . However, when magnesium is distributed relatively evenly on the surface of the base steel sheet, oxides are easily formed in the atmosphere, and the oxides flow down to cover the cross section, thereby blocking the cross section from the external corrosion environment or delaying the generation of rust.

In other words, magnesium at room temperature without moisture does not corrode well. However, when there is acid gas containing 300 ppm of CO ₂ and 1 ppm of SO ₂ in the atmosphere and 3MgCO ₃ .Mg (OH) ₂ .3H ₂ O (Hydromagnesite) and MgSO ₄ · 6H ₂ O are formed on the surface to protect the magnesium and dissolve in water, so that it flows easily and covers the cross section. In addition, magnesium in the aqueous solution forms a coating of Mg (OH) ₂ on the surface of the metal, and also protects the cross section by covering the cross section by dissolving in water. When the base is pH 10.5 or more, And the like. Thus, magnesium contributes to improving the corrosion resistance of the exposed portion of the base steel sheet at the cross section, although it may help a certain degree in improving the corrosion resistance.

Therefore, it is preferable that magnesium is added at a content ratio of 8.0 to 9.0% by weight, more preferably 8.3 to 8.6% by weight, of the total weight of the alloy coating layer. When the addition amount of magnesium is less than 8.0 wt% of the total weight of the alloy coating layer, the addition amount is insignificant and it is difficult to expect the above effect to be exhibited properly. On the contrary, when the addition amount of magnesium exceeds 9.0 wt% of the total weight of the alloy coating layer, the plating quality may be deteriorated due to the generation of a dross of the plating solution.

Silicon (Si)

Silicon (Si) is an element that is added to control the thickness of a brittle alloy coating layer by suppressing the strong reactivity of aluminum and to minimize the erosion of various metal structures in the plating bath and the dissolution of iron (Fe) from the base steel sheet. Depending on the content of silicon, the plating bath temperature, the inlet temperature of the base steel, and the structure of the coating layer may be changed, which may affect the quality and workability of the product.

The silicon is preferably added in an amount of 4.0 to 5.0% by weight, more preferably 4.5 to 4.8% by weight of the total weight of the alloy coating layer.

When the amount of silicon added is less than 4.0 wt% of the total weight of the alloy coating layer, the melting temperature must be increased to maintain the temperature of the plating bath at a high level. Since the reactivity of aluminum with iron is not restrained, rapid surface erosion of the steel surface occurs, To be subject to direct corrosion by On the other hand, when the addition amount of silicon exceeds 5.0% by weight of the total weight of the molten Al-Mg-Si alloy coating layer, much silicon of the rod-like form is precipitated in the plating layer to decrease the workability, Is lowered.

Aluminum (Al)

Aluminum (Al) contributes to improvement in corrosion resistance and also contributes to suppressing the formation of dross in the plating liquid.

It is preferable that the aluminum is added to the entire weight of the alloy coating layer except for the magnesium (Mg) and silicon (Si). That is, it is preferable that aluminum is added in a content ratio of 86 to 88% by weight of the total weight of the alloy coating layer.

If the added amount of aluminum is less than 86% by weight of the total weight of the alloy coating layer, it may be difficult to exhibit the above effect properly. On the contrary, when the addition amount of aluminum exceeds 88 wt% of the total weight of the alloy coating layer, adhesion and weldability may be deteriorated.

The alloy coating layer having the above composition preferably has a plating adhesion amount of 50 to 100 g / m < 2 >. More preferably, the alloy coating layer has a thickness of 10 to 30 mu m. At this time, the thickness of the alloy coating layer can be controlled by an air knife or the like. If the thickness of the alloy coating layer is less than 10 mu m, it may be difficult to ensure sufficient sacrificial corrosion resistance because the thickness is too thin. On the contrary, when the thickness of the alloy coating layer exceeds 30 탆, the corrosion-resistant period in which the base steel sheet can be sacrificed can be prolonged. However, since the excessive use of the plating solution can increase the manufacturing cost of the steel sheet, It is not economical.

2 is a process flow chart schematically showing a method of manufacturing a molten aluminum-based plated steel sheet according to an embodiment of the present invention.

Referring to FIG. 2, the method of manufacturing a molten aluminum-based plated steel sheet according to an embodiment of the present invention may include a base steel sheet immersion step (S210) and an alloy coating layer formation step (S220).

Base steel sheet immersion

In the base steel sheet immersion step (S210), the base steel sheet is immersed in a plating bath containing an aluminum-based plating solution composed of 8.0 to 9.0 wt% of magnesium (Mg), 4.0 to 5.0 wt% of silicon (Si) .

At this time, it was experimentally proven that the aluminum-based plating solution is composed of 8.3 to 8.6 wt% of magnesium (Mg), 4.5 to 4.8 wt% of silicon (Si) and the balance of aluminum (Al) Respectively. As the base steel sheet, any of hot-rolled steel sheets, cold-rolled steel sheets, and the like can be used without limitation.

The plating bath may have a hexahedral shape with the top open, but it is not limited thereto, and may have various shapes such as a cylindrical shape with the top open.

Alloy Coating Layer Formation

In the alloy coating layer formation step S220, the base steel sheet is taken out from the plating bath, and an alloy coating layer is formed on the surface of the base steel sheet so as to be coated with a plating adhesion amount of 50 to 100 g / m < 2 >.

At this time, the drawing temperature in the plating bath is preferably 590 to 650 ° C. The entering temperature in the plating bath can be defined as the temperature inside the plating bath when the base steel sheet is charged into the plating bath. In the present invention, the pull-in temperature in the plating liquid is carried out at 590 to 650 占 폚, which corresponds to a relatively low temperature region. This is because the ternary plating solution of Al-Mg-Si is strictly controlled in the above- It is understood that the melting point becomes closer to the point and the melting point becomes lower.

In this step, if the drawing temperature in the plating bath is less than 590 캜, the coating solution may not be smoothly coated on the surface of the base steel sheet due to insufficient fluidity of the plating solution, resulting in poor coating. On the other hand, if the drawing temperature in the plating bath exceeds 650 캜, it may act as a factor for hindering the plating adhesion.

In this step, in the process of removing the base steel sheet from the plating bath, the thickness of the alloy coating layer is adjusted to 10 to 30 占 퐉 by the air knife mounted on the top of the plating bath.

The molten aluminum-based plated steel sheet excellent in sacrificial corrosion resistance produced in the above-described processes (S210 to S220) is obtained by immersing the base steel plate in an aluminum-based plating solution composed of a ternary system of Al-Mg-Si having an optimized composition ratio, By forming the alloy coating layer so as to coat the surface with the plating adhesion amount of 50 to 100 g / m 2, excellent sacrificial corrosion resistance can be ensured.

In addition, since the present invention uses a ternary system of Al-Mg-Si plating solution at an optimized composition ratio, the melting point is lowered and the hot dip coating operation can be facilitated.

Example

Hereinafter, the configuration and operation of the present invention will be described in more detail with reference to preferred embodiments of the present invention. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.

The contents not described here are sufficiently technically inferior to those skilled in the art, and a description thereof will be omitted.

1. Manufacture of molten Al-Mg-Si system plating specimens

Table 1 shows composition ratios of the molten aluminum plating solution to the molten Al-Mg-Si based plating specimens prepared according to Examples 1 to 8 and Comparative Examples 1 to 4. At this time, the molten Al-Mg-Si-based plating specimens according to Examples 1 to 8 and Comparative Examples 1 to 4 were similarly used as base steel plates with cold-rolled steel sheets having a thickness of 30 mm. Subsequently, the base steel sheet was immersed in a plating bath filled with a molten aluminum plating solution having a composition shown in Table 1 at a pulling temperature of 620 DEG C, taken out from the plating bath, and coated on the surface thereof with a plating adhesion amount of 700 g / Mg-Si-based plating specimens each having an alloy coating layer of Al-Mg-Si were prepared.

[Table 1] (unit:% by weight)

2. Property evaluation

Table 2 shows the results of physical properties evaluation of the molten Al-Mg-Si-based plating specimens according to Examples 1 to 8 and Comparative Examples 1 to 3.

(1) Evaluation of corrosion resistance

The corrosion resistance was measured by spraying a brine continuously on the cross section of the plating specimen prepared using the plating solution according to Examples 1 to 8 and Comparative Examples 1 to 4 according to the method defined in ASTM B117 to measure the resistance time .

◎: over 1500 hours (very good)

○: 1000 hours or more, less than 1500 hours (excellent)

DELTA: 500 hours or more, less than 1000 hours (usually)

X: Less than 500 hours (bad)

(2) Evaluation of adhesion

The adhesion was evaluated by a method of observing whether or not the coating layer was peeled off after deforming the base steel plate and plated portion by pressing with a flange according to the drawing test method specified in KS D0254.

◎: No peeling of coating layer (excellent)

○: Fine peeling of coating layer (Excellent)

DELTA: slight peeling of the coating layer occurred (usually)

X: peeling of the entire coating layer (defective)

(3) Dross generation

The dross generation was evaluated by measuring the mass per unit area (g / m ² ) after removing the surface of the plating solution for 30 minutes in the atmosphere.

(4) Evaluation of heat resistance

Heat resistance was evaluated by the amount of oxidation of the coating layer and the discoloration time of the coating surface layer. In order to evaluate the heat resistance, the specimens according to Examples 1 to 8 and Comparative Examples 1 to 4 were heated to 800 DEG C and after 1000 hours, the weight difference before and after the test was evaluated in terms of oxidized amount. Was evaluated as the time at which visible discoloration was noticeably observed.

[Table 2]

Referring to Table 2, it can be confirmed that the plating specimens according to Examples 1 to 8 are excellent in corrosion resistance and adhesion. Particularly, in the case of the molten Al-Mg-Si based alloy plating specimens according to Examples 1 to 8, corrosion resistance against cross-sectional corrosion, which provides sacrificial corrosion resistance, is superior to those of Comparative Examples 1 to 4.

In the case of the molten Al-Mg-Si based alloy plating specimens according to Examples 1 to 8, the amount of dross generation was 157 to 276 g / m ² .

Particularly, in the case of the specimens of molten Al-Mg-Si based alloys according to Examples 5 to 7, the specimens exhibited better corrosion resistance and adhesion than Examples 1 to 4 and 8.

On the other hand, in the case of Comparative Examples 1 and 4 in which magnesium and silicon were out of the range suggested by the present invention, the adhesion was good, but the corrosion resistance was poor and the amount of dross generation was larger than that in Example 1. Further, in the case of Comparative Examples 2 and 3, all of the corrosion resistance, the adhesion property and the amount of dross generation were significantly lower than those of Example 1.

On the other hand, as a result of the evaluation of the heat resistance, in the case of the plated specimens according to Examples 1 to 8, the oxidation amount was measured to be 2000 mg or less, and the discoloration did not proceed for a long time exceeding 30 hours. On the other hand, in the case of the plated specimens according to Comparative Examples 1 to 4, the oxidation amount was measured to exceed 3000 mg, and the discoloration progressed within 30 hours.

Based on the above experimental results, it was confirmed that the plating specimens according to Examples 1 to 8, particularly Examples 5 to 7, exhibited the best properties in heat resistance.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. Such changes and modifications are intended to fall within the scope of the present invention unless they depart from the scope of the present invention. Accordingly, the scope of the present invention should be determined by the following claims.

100: molten aluminum-based plated steel sheet
120: Base steel plate
140: alloy coating layer
S210: Base steel sheet immersion step
S220: Alloy coating layer forming step

Claims (7)

1. A molten aluminum-based plated steel sheet comprising a base steel sheet and an alloy coating layer coated on the surface of the base steel sheet,
The alloy coating layer
Magnesium (Mg): 8.0 to 9.0 wt%,
Silicon (Si): 4.0 to 5.0 wt% and
And the remaining aluminum (Al).
The method according to claim 1,
The alloy coating layer
Magnesium alloy, aluminum, aluminum, aluminum, magnesium, magnesium, silicon, and the like.
The method according to claim 1,
The alloy coating layer
And has a plating adhesion amount of 50 to 100 g / m < 2 >.
The method according to claim 1,
The alloy coating layer
And a thickness of 10 to 30 占 퐉.
(a) immersing a base steel sheet in a plating bath containing an aluminum based plating solution composed of 8.0 to 9.0 wt% of magnesium (Mg), 4.0 to 5.0 wt% of silicon (Si) and the balance of aluminum (Al) And
(b) removing the base steel sheet from the plating bath to form an alloy coating layer on the surface of the base steel sheet so as to be coated with a plating adhesion amount of 50 to 100 g / m < 2 > .
6. The method of claim 5,
In the step (a)
Wherein the drawing temperature in the plating bath is 590 to 650 占 폚.
6. The method of claim 5,
In the step (a)
Wherein the aluminum-based plating solution is composed of magnesium (Mg): 8.3 to 8.6 wt%, silicon (Si): 4.5 to 4.8 wt%, and the balance aluminum (Al).

Images