JP7796878B2 - Solution composition for steel sheet surface treatment, steel sheet surface treated with the same, and method for manufacturing the same - Google Patents

Description

The present invention relates to a solution composition that can improve the pitting corrosion resistance and blackening resistance of steel sheets, a steel sheet surface-treated using the same, and a method for producing the steel sheet.

Highly corrosion-resistant hot-dip plated steel, which has a coating layer containing zinc (Zn), magnesium (Mg), and aluminum (Al), is known for its excellent red rust corrosion resistance.

However, because the exposed surfaces of such highly corrosion-resistant hot-dip galvanized steel products are mostly composed of zinc or zinc alloys, they are prone to developing spot-like corrosion defects on the surface when exposed to general environments, particularly humid atmospheres, resulting in a poor appearance. Furthermore, in recent years, foreign matter defects have also been occurring in which the coating layer of the hot-dip galvanized steel product adheres to the rolls as it passes through them during processing.

To solve these problems, hexavalent chromium or chromate treatment has traditionally been applied to plated steel sheets to ensure corrosion resistance and blackening resistance. However, hexavalent chromium has been designated as a hazardous environmental substance, and regulations on its use are currently being strengthened. Furthermore, when hexavalent chromium is used as a surface treatment agent for plated steel sheets, there are defects such as the surface of the steel sheet turning black or black spots appearing.

Currently, a method has been developed in which a surface treatment solution composition containing trivalent chromium is coated onto plated steel sheets to ensure the plated steel sheets' corrosion resistance and blackening resistance.

For example, Patent Document 1 applies a chemical conversion treatment method in which steel sheets are immersed in a composition containing trivalent chromium. However, this method has problems, such as the deposition time being too long to be applied to the continuous processes of steel companies, and the chemical conversion treatment method impairs the fingerprint resistance of the steel sheets.

Meanwhile, Patent Documents 2 and 3 disclose that coating a composition containing trivalent chromium onto plated steel sheets using a spray or roll coater method makes it possible to apply the composition to continuous production lines at steel companies and ensure fingerprint resistance. However, because these compositions contain porous silica components, they are not suitable for Mg- and Al-based alloys, which tend to discolor rapidly in humid atmospheres. Furthermore, porous silica has strong hygroscopic properties, which can cause rapid discoloration in Zn-Mg-Al-based alloy steel sheets.

Korean Patent Publication No. 10-2009-0024450 Korean Patent Publication No. 10-2004-0046347 Japanese Patent Publication No. 2002-069660

One embodiment of the present invention improves the pitting corrosion resistance and blackening resistance of a steel sheet by controlling the composition of a coating solution applied to the surface of a highly corrosion-resistant plated steel sheet. It provides a solution composition with excellent solution stability, and provides a surface-treated steel sheet and a method for manufacturing the same.

The objectives of the present invention are not limited to the above. The objectives of the present invention can be understood from the overall content of this specification, and a person with ordinary skill in the art to which the present invention pertains will have no difficulty in understanding the additional objectives of the present invention.

One embodiment of the present invention provides a solution composition for treating steel sheet surfaces, comprising: (a) 20 to 60% by weight of a trivalent chromium compound; (b) 0.1 to 10% by weight of an acidity regulator; (c) 1 to 20% by weight of an adhesion improver; (d) 1 to 20% by weight of a corrosion resistance improver; (e) 0.01 to 3.0% by weight of a pitting corrosion improver; (f) 1 to 20% by weight of a cosolvent; and (g) the balance being a solvent.

Another embodiment of the present invention provides a surface-treated plated steel sheet comprising a steel sheet, a Zn-Mg-Al-based plating layer formed on at least one surface of the steel sheet, and a surface treatment coating layer formed on the plating layer, wherein the surface treatment coating layer is a coating layer formed from the solution composition described above.

Another embodiment of the present invention provides a method for producing a surface-treated plated steel sheet, including the steps of: hot-dip galvanizing at least one surface of a steel sheet to form a Zn-Mg-Al-based plating layer; coating the plating layer with the above-described solution composition; and drying the coated steel sheet.

The present invention provides a solution composition that exhibits excellent solution stability and does not exhibit precipitation or aggregation even when used after long-term storage. By coating this solution composition onto a steel sheet, a steel sheet with excellent pitting corrosion resistance and blackening resistance can be provided.

In addition, it also improves product lifespan by improving foreign matter defects during the coating process.

1 shows a plated steel sheet (a) on which pitting corrosion (at edges) has occurred and a plated steel sheet (b) on which no surface corrosion has occurred, in one embodiment of the present invention.

The inventors of the present invention conducted extensive research to find a solution composition that is advantageous for coating steel sheets, such as highly corrosion-resistant hot-dip plated steel sheets, to improve not only the pitting corrosion resistance of the coated steel sheets but also their resistance to blackening.

As a result, it is possible to provide a solution composition that contains a trivalent chromium compound, an acidity regulator, an adhesion improver, a corrosion resistance improver, a pitting corrosion improver, and a co-solvent in appropriate amounts, and this solution composition has high solution stability. The researchers confirmed that the intended effects can be achieved when such a solution composition is used to treat the surface of steel sheet, leading to the completion of the present invention.

The present invention is described in detail below.

First, we will specifically describe the solution composition for steel sheet surface treatment according to one embodiment of the present invention.

The solution composition according to the present invention can contain (a) 20 to 60% by weight of a trivalent chromium compound, (b) 0.1 to 10% by weight of an acidity regulator, (c) 1 to 20% by weight of an adhesion improver, (d) 1 to 20% by weight of a corrosion resistance improver, (e) 0.01 to 3.0% by weight of a pitting corrosion improver, (f) 1 to 20% by weight of a cosolvent, and (g) the balance being solvent.

The content of the solution composition of the present invention is based on a total of 100% by weight.

As will be described in detail below, the solution composition can form a coating layer on at least one surface of a substrate to which the composition can be applied. In the present invention, the substrate can be the above-mentioned steel sheet, for example, a highly corrosion-resistant hot-dip plated steel material, and a non-limiting example thereof can be a Zn-Mg-Al alloy plated steel sheet.

The following describes in detail each component that makes up the above solution composition.

(a) 20 to 60% by weight of trivalent chromium compounds

In the solution composition of the present invention, the trivalent chromium compound primarily forms an insoluble coating on the surface of the steel sheet, improving corrosion resistance through its barrier effect.

If the content of the trivalent chromium compound in the solution composition of the present invention is less than 20%, a robust insoluble coating cannot be formed sufficiently, and the moisture penetrating the surface of the steel sheet cannot be effectively blocked, resulting in failure to ensure corrosion resistance. On the other hand, if the content exceeds 60%, there is a risk of foreign matter defects occurring due to the excessive chromium content.

In the present invention, the type of trivalent chromium compound is not particularly limited, but preferably is one or more selected from the group consisting of chromium sulfate, chromium nitrate, chromium phosphate, chromium fluoride, chromium chloride, and mixtures thereof.

(b) Acidity regulator: 0.1 to 10% by weight

In the solution composition of the present invention, the acidity regulator adjusts the pH of the solution so that the components in the composition remain stable in the solution and react appropriately under coating conditions to form a stable coating.

If the content of such an acidity regulator is less than 0.1%, the pH of the solution may increase, reducing solution stability. On the other hand, if the content exceeds 10%, residual acid after drying may make it impossible to ensure corrosion resistance, etc.

In the present invention, the type of the acidity regulator is not particularly limited, but is preferably _one or more _{selected from the group consisting of phosphoric acid, nitric acid, sulfuric acid, hydrofluoric acid, hydrochloric acid, (NH4)H2PO4, (NH4)2HPO4, NaH2PO4, Na2HPO4 , phytic acid , glycolic acid , lactic} acid, acetic acid, oxalic acid, and mixtures thereof.

(c) Adhesion improver: 1 to 20% by weight

In the solution composition of the present invention, the adhesion improver bonds with the trivalent chromium compound and the like, and also bonds with the steel sheet, thereby improving the adhesion and corrosion resistance of the coating layer.

If the content of such adhesion improvers is less than 1%, sufficient adhesion to the steel sheet may not be ensured, which may result in foreign matter defects. On the other hand, if the content exceeds 20%, an excessive amount may remain after the coating film is formed, which may make it impossible to ensure corrosion resistance, etc.

In the present invention, there are no particular limitations on the type of adhesion improver, but preferred are vinyl methoxy silane, vinyl trimethoxy silane (VTMS), vinyl epoxy silane, vinyl triepoxy silane, 3-aminopropyl triepoxy silane, 3-glycidoxypropyl trimethoxy silane, 3-metaglyoxypropyl trimethoxy silane, γ-glycidoxypropyl triethoxy silane, γ-glycidoxytrimethyl dimethoxy silane, N-(3-(trimethoxysilyl)propyl)ethy lenediamine (AEAPTMS), 2-(3,4-Epoxycyclohexyl)ethyltrimethox ysilane, 2-(3,4-Epoxycyclohexyl)ethyltriethoxysilane, 3-(2,3- Epoxypropoxy)propyltrimethoxysilane, 3-(2,3-Epoxypropoxy)pr opyltriethoxysilane, 3-(2,3-Epoxypropoxy)propylmethyldiethox ysilane, 3-(2,3-Epoxypropoxy)propylmethyldimethoxysilane, 3- Aminopropyltriethoxysilane, 3-Aminopropyltrimethoxysilane, 3- Aminopropylmethyldiethoxysilane, N-(2-Aminoethyl-3-aminopro pyl) methyldimethoxysilane, N-(2-Aminoethyl-3-aminopropyl)tri It can be one or more selected from the group consisting of trimethylsilane, diethylentriaminopropyltrimethoxysilane, 3-ureidopropyltrimethoxysilane, N-phenylaminopropyltrimethoxysilane, (3-glycidyloxypropyl)trimethoxysilane (GPTMS), methyltrimethoxysilane (MTMS), and mixtures thereof.

(d) Corrosion resistance improver: 1 to 20% by weight

In the solution composition of the present invention, the corrosion resistance improver fills any gaps that may exist between the trivalent chromium compound and the adhesion improver, forming a passivation film and suppressing corrosion.

If the content of such corrosion resistance improvers is less than 1%, it will be difficult to ensure corrosion resistance because a sufficient passive film cannot be formed. On the other hand, if the content exceeds 20%, the excessively high solids content may reduce solution stability.

In the present invention, the type of corrosion resistance improver is not particularly limited, but is preferably one or more selected from the group consisting of vanadyl acetylacetonate, ammonium metavanadate, potassium metavanadate, sodium metavanadate, vanadium trioxide, vanadium acetylacetate, ammonium metavanadate, silicon oxide, and mixtures thereof.

(e) 0.01 to 3.0% by weight of pitting corrosion improver
In the solution composition of the present invention, the pitting corrosion improver, together with the corrosion resistance improver, prevents localized penetration of corrosive factors and minimizes pitting corrosion that occurs in the form of spots.

In the solution composition of the present invention, if the content of the pitting corrosion ameliorator is less than 0.01%, the local penetration of corrosion factors cannot be blocked, resulting in the problem of pitting corrosion. On the other hand, if the content exceeds 3.0%, the pH of the solution may rise excessively, reducing solution stability.

In the present invention, the type of the pitting corrosion improver is not particularly limited, but is preferably one or more selected from the group consisting of ethylenediamine, hexamethylenediamine, trimethylamine, methylamine, diphenylamine, ethyleneamine, aniline, toluidine, piperidine, aziridine, pyridine, alanine, propylamine, diisopropylamine, monoisopropylamine, dibutylamine, dipropylamine, and mixtures thereof.

(f) Cosolvent: 1 to 20% by weight

In the solution composition of the present invention, the cosolvent adjusts the evaporation rate of the solvent during the drying process during the coating operation and plays a role in suppressing defects on the coating surface after drying.

If the content of such co-solvents is less than 1%, they are insufficient in regulating the evaporation rate during drying, causing the main solvent to boil rapidly at its boiling point, resulting in a surface defect known as popping, which can lead to problems such as reduced corrosion resistance. On the other hand, if the content exceeds 20%, the solution's viscosity and density may change suddenly, potentially reducing solution stability.

In the present invention, the type of co-solvent is not particularly limited, but is preferably one or more selected from the group consisting of ethanol, isopropyl alcohol, methanol, tallow alcohol, 2-butoxyethanol, diethylene glycol monobutyl ether, and mixtures thereof.

(g) Solvent

The solution composition of the present invention may contain a solvent as the remaining component, and in the present invention, water (distilled water, deionized water) may be used as the solvent.

The following provides a detailed description of another embodiment of the present invention, a surface-treated steel sheet including a coating layer that has been surface-treated with the above-described solution composition.

In the present invention, the above composition can be used to apply a surface treatment to a galvanized steel sheet, preferably a ternary (Zn-Mg-Al) hot-dip galvanized steel sheet.

That is, the surface-treated steel sheet of the present invention can include a steel sheet, a Zn-Mg-Al-based plating layer formed on at least one surface of the steel sheet, and a surface treatment coating layer formed on the plating layer.

The steel sheet referred to here is a base steel sheet from which a plated steel sheet can be obtained, and in particular, any steel sheet from which a ternary (Zn-Mg-Al) hot-dip galvanized steel sheet can be obtained.

The Zn-Mg-Al-based plating layer may contain, in weight percent, 4.0 to 7.0% magnesium (Mg), 11.0 to 19.5% aluminum (Al), the remainder Zn, and other unavoidable impurities.

The magnesium (Mg) in the coating layer is an element that improves the corrosion resistance of the coated steel sheet, and in order to ensure the excellent corrosion resistance aimed at in the present invention, its content is preferably 4.0% or more. However, if the Mg content is excessive, there is a risk of dross being generated in the coating bath, and there is a risk of forming excessive intermetallic compounds with high hardness in the coating layer, which may deteriorate the bendability of the steel sheet. Therefore, the Mg content can be limited to 7.0%.

However, adding Mg at a content of 4.0% or more poses the risk of dross formation due to Mg oxidation in the coating bath. Taking this into consideration, it is preferable to include aluminum (Al) at a content of 11.0% or more. However, if the Al content is excessive, the melting point of the coating bath will increase, which will result in excessively high operating temperatures, potentially causing problems with high-temperature operation, such as erosion of the coating bath structures and denaturation of the steel sheet. Therefore, it is preferable to limit the Al content to 19.5% or less.

The remainder of the composition, excluding the above Mg and Al, is zinc (Zn), and unintended unavoidable impurities may be mixed in during the manufacturing process of plated steel sheets with a Zn-Mg-Al-based plating layer. It should be made clear that the meaning of "unavoidable impurities" is easily understood by anyone skilled in the relevant technical field.

It is preferable that the structure of the above-mentioned Zn-Mg-Al-based plating layer satisfy the following [Relationship 1].

[Relationship 1]
0.26≦I(110)/I(103)≦0.65
(In Relational Formula 1, I(110) represents the X-ray diffraction integrated intensity of the (110) crystal plane peak in the MgZn ₂ phase, and I(103) represents the X-ray diffraction integrated intensity of the (103) crystal plane peak in the MgZn ₂ phase.)

In the present invention, the MgZn _two- phase of the Zn—Mg—Al-based plating layer is controlled according to the above [Relational Formula 1], thereby ensuring the bendability, whiteness, etc. of the plated steel sheet.

If the value defined by the above [Relational Formula 1] is less than 0.26, the proportion of (103) crystals in the MgZn ₂ phase relative to the (110) crystals in the MgZn ₂ phase is excessive, which may result in insufficient bendability and whiteness. On the other hand, if the value exceeds 0.65, the proportion of (110) crystals in the MgZn ₂ phase relative to the (103) crystals in the MgZn ₂ phase is too high, which may result in an inability to induce an increase in diffuse reflection and insufficient whiteness.

In this case, the integrated intensity value of I(110) may range from 120 to 200, and the integrated intensity value of I(103) may range from 240 to 300. In this way, it is preferable to satisfy the value of [Relationship 1] above within each range.

A coating layer formed by coating the composition of the present invention in solution form may be included on top of the Zn-Mg-Al-based plating layer. In this case, the coating layer preferably has a thickness of 0.1 to 2.0 μm.

If the thickness of the coating layer is less than 0.1 μm, the surface treatment solution composition will be applied too thinly to the roughness peaks present on the surface of the plated steel sheet, resulting in reduced corrosion resistance. On the other hand, if the thickness exceeds 2.0 μm, the coating layer will be too thick, resulting in poor workability and increased solution treatment costs, which is economically disadvantageous.

Here, the above thickness refers to the thickness after drying.

Furthermore, the present invention describes a method for producing surface-treated steel sheets using the above composition.

More specifically, the method may include the steps of: hot-dip galvanizing at least one surface of a steel sheet to form a Zn-Mg-Al-based plating layer; applying the composition of the present invention in solution onto the plating layer to perform a coating process; and drying the coated steel sheet.

When applying the composition of the present invention in solution to the steel sheet, any commonly used coating method can be used, and there are no particular limitations.

For example, the coating process can be carried out by selecting one of the following methods: bar coating, roll coating, spraying, deposition, spray squeegee, deposition squeegee, etc.

The drying process for the steel sheet coated with the above composition is preferably carried out at a temperature range of 40 to 280°C, based on the final temperature reached (PMT) of the base steel sheet (steel sheet).

If the final temperature of the base steel plate is less than 40°C, the formation of a robust coating structure may be insufficient, resulting in poor corrosion resistance and blackening resistance. On the other hand, if the temperature exceeds 280°C, the hardness of the coating may increase excessively, deteriorating the corrosion resistance of the processed area and potentially causing deterioration in surface quality, such as yellowing due to excessive heat.

After the above drying process is complete, the steel sheet can have a coating layer with a thickness of 0.1 to 2.0 μm after drying.

In the present invention, the means for performing the drying process is not particularly limited, but it should be noted that equipment such as an induction oven or a hot air drying furnace can be used, and the conditions for such equipment may be the same as those used under normal conditions.

The present invention will now be described in more detail through examples. However, the description of these examples is intended to illustrate the implementation of the present invention, and the present invention is not limited by the description of these examples. The scope of the present invention is determined by the matters set forth in the claims and matters that can be reasonably inferred therefrom.

[Production of solution composition for steel sheet surface treatment]
In order to measure the physical properties of the solution composition for surface treatment of steel sheet according to the present invention, the solution composition was prepared using the following materials.

First, phosphoric acid was added to distilled water (solvent) as an acidity regulator, and then chromium nitrate, a trivalent chromium compound, was added at approximately 40°C and stirred for approximately 30 minutes. Using a similar method, the adhesion promoter (3-glycidyloxypropyl)trimethoxysilane (GPTMS), the corrosion resistance improver silicon oxide, the pitting corrosion improver ethylenediamine, and the co-solvent ethanol were added at 30-minute intervals while stirring.

The content of each component is shown in Table 1 below.

Solution Stability In order to confirm whether the prepared solution composition maintains its stability under certain conditions, the following experiment was carried out.

After measuring the initial viscosity (Vi) of each solution composition in Invention Examples 1 to 12 and Comparative Examples 1 to 12, the composition was stored in a 50°C oven for 120 hours, cooled to 25°C, and the viscosity (VI) at 25°C was measured. The measured viscosity values were substituted into Equation 1 below to calculate the value (ΔV), which was used to evaluate the solution stability. The results are shown in Table 3 below.

[Mathematical formula 1]
△V=(Vl-Vi)/Vi×100(%)

<Evaluation criteria for solution stability>
○: ΔV value is less than 20(%), or no gelation phenomenon is observed when visually observed. ×: ΔV value is 20(%) or more, or gelation phenomenon is observed when visually observed.

[Production of surface-treated steel sheets]
The solution composition was then applied to the surface of a steel sheet by bar coating, followed by drying in an induction oven to obtain a surface-treated steel sheet. The bar coating was performed so that the coating weight of the composition was approximately 35 mg/ ^m2 based on Cr.

The steel sheet used for applying the solution composition was a Zn-Mg-Al alloy hot-dip galvanized steel sheet (plating layer: Mg 5.4 wt%, Al 12.6 wt%, balance Zn and unavoidable impurities, value of [Relationship 1]: 0.40). It was cut into 7 cm x 15 cm (width x length) and degreased to prepare test specimens.

The drying temperature during the above surface treatment and the thickness of the formed coating layer are shown in Table 2 below.

To measure the physical properties of the surface-treated steel sheets manufactured as described above, the following methods and standards were used to measure plate corrosion resistance, processed area corrosion resistance, pipe-making oil corrosion resistance, alkali resistance, pitting corrosion resistance, foreign matter defects, etc. The results are shown in Table 3 below.

Plate Corrosion Resistance Each steel plate (test piece) was treated with the solution composition according to the method specified in ASTM B117, and then the rate of white rust formation on the steel plate over time was measured.

<Evaluation criteria for plate corrosion resistance>
○: White rust occurrence time is 144 hours or more △: White rust occurrence time is 96 hours or more but less than 144 hours ×: White rust occurrence time is less than 96 hours

Corrosion Resistance of Processed Part The surface-treated steel sheet (test piece) was pushed up to a height of 6 mm using an Erichsen tester, and the degree of white rust formation after 24 hours was measured.

<Evaluation criteria for corrosion resistance of processed parts>
○: White rust does not occur, or if it does occur, it is very fine. △: White rust occurs in the circle and some of it has flowed away, but not outside. ×: White rust occurs and has flowed outside the circle.

The steel sheets (test pieces) surface-treated as described above were immersed in pipe-making oil at room temperature for 24 hours, and the color difference before and after immersion was measured. The pipe-making oil used was BW WELL MP-411 from Buhmwoo Co., Ltd., Korea, diluted with 10% water.

<Evaluation criteria for pipe-making oil abrasion>
○: ΔE≦2
△: 2<ΔE≦3
×: 3<ΔE

The steel sheets (test pieces) surface-treated as described above were immersed in a degreasing solution at 60°C for 2 minutes, rinsed with water, and air-blowed, and the color difference before and after was measured. The alkaline degreasing solution used was Parkerizing's Finecleaner L 4460 A: 20 g/2.4 L + L 4460 B: 12 g/2.4 L (pH = 12).

<Evaluation criteria for alkali resistance>
○: ΔE≦2
△: 2<ΔE≦4
×: 4<ΔE

Pit-like Corrosion Resistance Two steel sheets (test pieces) that had been surface-treated as described above were sprayed with dew, then the sprayed steel sheets were butted together, packaged, and placed in a thermo-hygrostat, where a total of eight cycles were performed, consisting of six hours at high temperature (42°C, 95%) and six hours at low temperature (15°C, 60%). The number of pit-like defects on the surface was then measured. The scan area of the steel sheets was set to 150 x 50 ^mm² , and this was magnified 100 times to count only those with an area of corrosion pit-like defects of 29,500 ^µm² or more.

<Evaluation criteria for pitting corrosion resistance>
○: Number of dots≦20
△: 20<number of dots≦40
×: 40 < number of dots

Foreign Matter Defects To evaluate foreign matter defects on the surface-treated steel sheet (test piece) as described above, a probe having a surface area of approximately 4 ^cm2 was covered with white gauze, and a 10 kg weight was placed on the probe. The probe was rubbed back and forth against the surface of the steel sheet 100 times, and the whiteness values of the gauze before and after rubbing (ΔL = L _before - L _after ) were measured. In this case, the steel sheet and probe were placed in a humidity chamber to simulate high humidity conditions, and the humidity inside the chamber was maintained at 95% or more using a humidifier, and then the friction evaluation was performed.

<Evaluation criteria for foreign matter defects>
○: ΔL≦2.5
Δ: 2.5<ΔL≦5.0
×: 5.0<ΔL

As shown in Table 3 above, the solution compositions of Invention Examples 1 to 12 had excellent solution stability, and steel sheets surface-treated with these solution compositions also showed extremely excellent results in all evaluations.

In contrast, Comparative Example 1 had an insufficient content of trivalent chromium compounds, and the corrosion resistance provided by the barrier effect was insufficient, resulting in poor flat plate corrosion resistance, processed area corrosion resistance, and pitting corrosion resistance.

Comparative Example 2 shows that the content of trivalent chromium compounds was excessively high, resulting in the occurrence of foreign matter defects.

In Comparative Example 3, the content of the acidity regulator was insufficient, resulting in poor solution stability, and the steel plate surface-treated with this solution composition exhibited poor flat plate corrosion resistance, processed area corrosion resistance, and pitting corrosion resistance.

In Comparative Example 4, the content of the acidity regulator was excessive, resulting in a large amount of acid remaining in the solution, and the surface-treated steel sheet had poor flat plate corrosion resistance, processed area corrosion resistance, and pitting corrosion resistance.

In Comparative Example 5, the content of adhesion improver was insufficient, resulting in foreign matter defects.

In Comparative Example 6, the content of adhesion promoter was too high, and the remaining unreacted silane resulted in poor flat corrosion resistance, processed area corrosion resistance, and pitting corrosion resistance of the surface-treated steel sheet.

In Comparative Example 7, the content of the corrosion resistance improver was insufficient, resulting in insufficient corrosion resistance and poor flat plate corrosion resistance, processed area corrosion resistance, and pitting corrosion resistance.

In Comparative Example 8, the content of the corrosion resistance improver was excessive. The excessively high solid content resulted in poor solution stability, poor alkali resistance of the surface-treated steel sheet, and the occurrence of foreign matter defects.

In Comparative Example 9, the content of the pitting corrosion improver was insufficient, and the surface-treated steel sheet had poor pitting corrosion resistance.

In Comparative Example 10, the content of the pitting corrosion improver was excessive, resulting in insufficient solution stability and poor corrosion resistance in the processed areas of the surface-treated steel sheet.

In Comparative Example 11, the cosolvent content was insufficient, and the surface-treated steel sheet exhibited poor flat plate corrosion resistance, processed area corrosion resistance, and pitting corrosion resistance.

In Comparative Example 12, the cosolvent content was excessive, resulting in insufficient solution stability and poor corrosion resistance in the processed areas of the surface-treated steel sheet.

Figure 1 shows the surface shape of a steel sheet (Example 1) that was surface-treated using the solution composition of the present invention, and the surface shape of a steel sheet that was surface-treated using a conventional composition.

As shown in Figure 1, the steel sheet (a) surface-treated with the conventional solution composition exhibited spot corrosion defects at the edges, whereas the steel sheet surface-treated with the solution composition of the present invention had a smooth surface all the way to the edges without any defects.

Claims (7)

(a) 20 to 60 wt. % of one or more trivalent chromium compounds selected from the group consisting of chromium sulfate, chromium nitrate, chromium phosphate, chromium fluoride, chromium chloride, and mixtures thereof;
(b) 0.1 to ₁₀ % by _weight of one _or more acidity _{regulators selected} from the group consisting of phosphoric acid, nitric acid, sulfuric acid, hydrofluoric acid, hydrochloric acid, ( _NH4 ) _H2PO4 , ( _NH4 ) _2HPO4 , _NaH2PO4 , Na2HPO4 , phytic acid, glycolic acid, lactic acid, acetic acid, oxalic acid, and mixtures thereof ;
(c) vinyl methoxy silane, vinyl trimethoxy silane (VTMS), vinyl epoxy silane, vinyl triepoxy silane, 3-aminopropyl triepoxy silane, 3-glycidoxypropyl trimethoxy silane, 3-metaglyoxypropyl trimethoxy silane, γ-glycidoxypropyl triethoxy silane, γ-glycidoxytrimethyl dimethoxy silane, N-(3-(trimethoxysilyl)propyl)ethylenediamine (AEAPTMS), 2-(3,4 -Epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-Epoxycyclohexyl)ethyltriethoxysilane, 3-(2,3-Epoxypropoxy)propyltrim ethoxysilane, 3-(2,3-Epoxypropoxy)propyltriethoxysilane, 3-(2,3-Epoxypropoxy)propylmethyldiethoxysilane, 3-(2,3-Epox ypropoxy)propylmethyldimethoxysilane, 3-Aminopropyltriethoxysilane, 3-Aminopropyltrimethoxysilane, 3-Aminopropylmet hyldiethoxysilane, N-(2-Aminoethyl-3-aminopropyl)methyldimethoxysilane, N-(2-Aminoethyl-3-aminopropyl)trimethoxysilane 1 to 20 wt. % of one or more adhesion promoters selected from the group consisting of methyltrimethoxysilane, diethylenetriaminopropyltrimethoxysilane, 3-ureidopropyltrimethoxysilane, N-phenylaminopropyltrimethoxysilane, (3-glycidyloxypropyl)trimethoxysilane (GPTMS), methyltrimethoxysilane (MTMS), and mixtures thereof ;
(d) 1 to 20 wt. % of one or more corrosion resistance improvers selected from the group consisting of vanadyl acetylacetonate, ammonium metavanadate, potassium metavanadate, sodium metavanadate, vanadium trioxide, vanadium acetylacetate, ammonium metavanadate, silicon oxide, and mixtures thereof;
(e) 0.01 to 3.0 wt. % of one or more pitting corrosion improvers selected from the group consisting of ethylenediamine, hexamethylenediamine, trimethylamine, methylamine, diphenylamine, ethyleneamine, aniline, toluidine, piperidine, aziridine, pyridine, alanine, propylamine, diisopropylamine, monoisopropylamine, dibutylamine, dipropylamine, and mixtures thereof ;
(f) 1 to 20 wt % of one or more co-solvents selected from the group consisting of ethanol, isopropyl alcohol, methanol, tallow alcohol, 2-butoxyethanol, diethylene glycol monobutyl ether, and mixtures thereof; and (g) the balance being water . Steel plate and
a Zn—Mg—Al-based plating layer formed on at least one surface of the steel sheet;
a surface treatment coating layer formed on the plating layer,
A surface-treated plated steel sheet, wherein the surface treatment coating layer is a coating layer formed from the composition of claim 1 . The Zn-Mg-Al-based plating layer contains, by weight %, 4.0 to 7.0% magnesium (Mg), 11.0 to 19.5% aluminum (Al), the balance being Zn, and other inevitable impurities;
The surface-treated plated steel sheet according to claim 2 , wherein the following relational expression 1 is satisfied:
[Relationship 1]
0.26≦I(110)/I(103)≦0.65
(In Relational Formula 1, I(110) represents the X-ray diffraction integrated intensity of the (110) crystal plane peak in the MgZn ₂ phase, and I(103) represents the X-ray diffraction integrated intensity of the (103) crystal plane peak in the MgZn ₂ phase.) 3. The surface-treated plated steel sheet according to claim 2 , wherein the surface treatment coating layer has a thickness of 0.1 to 2.0 μm. forming a Zn—Mg—Al-based coating layer on at least one surface of the steel sheet by hot-dip galvanizing;
coating the plating layer with the composition of claim 1 ;
and drying the coated steel sheet. 6. The method for producing a surface-treated plated steel sheet according to claim 5 , wherein the coating treatment is performed by any one method selected from the group consisting of bar coating, roll coating, spraying, deposition, spray squeegeeing, and deposition squeegeeing. The method for producing a surface-treated plated steel sheet according to claim 5 , wherein the drying is carried out at a temperature in the range of 40 to 280°C based on the final temperature (PMT) of the steel sheet.