KR20160071918A - Coating composition, and method for coating of steel using the same, and coating steel coated coating composition - Google Patents

Abstract

The present invention relates to a plating composition, a plated steel member plating method using the same, and the plated steel member plated with the plating composition. The plating composition comprises: 35-55 wt% of Zn; 0.3-2 wt% of Mg; 0.5-3 wt% of Si; and the remaining consisting of Al with the total weight thereof. The plating composition satisfies an equation 1 and an equation 2; wherein equation 1 is 0.9 <= Al (wt%)/Zn (wt%) <= 1.8, and equation 2 is Si (wt%) < Al (wt%) × 0.03 + Mg (wt%) × 0.7. The present invention obtains an effect of plating the plated steel member (Al-Zn based alloy plated steel member) with excellent corrosion resistance, excellent machinability, and excellent plated surface flatness.

Description

TECHNICAL FIELD [0001] The present invention relates to a plating composition, a method for producing the coated steel using the same, and a coated steel coated with the plating composition,

The present invention relates to a plating composition, a method for producing a plated steel material using the same, and a plated steel material coated with the plating composition, and more particularly, to an Al-Zn based alloy plating composition having excellent corrosion resistance, The present invention relates to a method of producing a plated steel material and a plated steel material coated with the plated composition.

Zinc-plated steel sheets, which have a higher ionization tendency than iron, have been used for a long time since they have excellent corrosion resistance to prevent corrosion of iron. Currently, galvanized steel sheets are widely used in the fields of automobiles, household appliances and building materials.

However, the demand for the improvement of the corrosion resistance of the zinc-plated steel sheet used in the building materials field is increasing as the consumer's desire level increases.

In the late 1960s, an Al-Zn-plated steel sheet called Galvalume was developed and used as a corrosion-resistant steel sheet for construction materials. However, the corrosion resistance of Al-Zn coated steel sheet is superior to that of conventional galvanized steel sheet,

Prior art related to this is Korean Patent No. 10-1091341 (Dec. 24, 2011) _ "composition for steel sheet coating excellent in processability, adhesiveness, weldability and alkali-debonding property, and zinc or zinc alloy-plated steel sheet".

The present invention provides a plating composition, a method of manufacturing a plated steel material using the same, and a plated steel material coated with the plating composition.

In order to solve the above-described problems, the plating composition preferably contains 35 to 55 wt% of Zn, 0.3 to 2 wt% of Mg, 0.5 to 3 wt% of Si, and the balance of Al based on the total weight of the plating composition, It is an object of the present invention to provide a plating composition satisfying the condition of the formula (2).

[Equation 1]

0.9? Al (wt%) / Zn (wt%)? 1.8

&Quot; (2) &quot;

Si (wt%) <Al (wt%) x 0.03 + Mg (wt%) x 0.7

 Another object of the present invention is to provide a plating composition which is effective for improving corrosion resistance, workability, and excellent plating surface property, a method for manufacturing a plated steel material using the same, and a plated steel material coated with the plating composition.

Other objects and advantages of the present invention will become more apparent from the following detailed description of the invention and claims.

For a complete understanding of the present invention, various specific details are set forth, such as specific forms, compositions, and processes, and the like. However, certain embodiments may be practiced without one or more of these specific details, or with other known methods and forms. In other instances, well-known processes and techniques of manufacture are not described in any detail, in order not to unnecessarily obscure the present invention. Reference throughout this specification to "one embodiment" or "embodiment" means that a particular feature, form, composition, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Accordingly, the appearances of the phrase " in one embodiment "or" the embodiment "in various places throughout this specification are not necessarily indicative of the same embodiment of the present invention. In addition, a particular feature, form, composition, or characteristic may be combined in any suitable manner in one or more embodiments.

In the present invention, a polygonal image means a shape of a figure surrounded by three or more line segments. For example, the shape of the polygonal image is not limited to a triangle, a rectangle, a pentagon, and a hexagon.

In the present invention, the Chinese character shape means Mg ₂ Si phase formed on the plating layer as shown in FIG. The Chinese character shape is the Mg ₂ Si phase which is formed when the process structure is formed with the Al phase in the sub-process composition.

In one embodiment, the present invention relates to a plating composition comprising 35 to 55 wt% of Zn, 0.3 to 2 wt% of Mg, 0.5 to 3 wt% of Si, and the balance Al relative to the total weight of the plating composition. The above composition substantially has the composition of the plating bath or the plating layer of the plated steel.

Specifically, the plating composition is a plating composition satisfying the following equations (1) and (2), more preferably a plating composition satisfying the following condition (3). The following equations (1) to (3) are derived from the relationships between the weights of Si, Al and Mg through a number of examples as in the case of the present invention.

[Equation 1]

0.9? Al (wt%) / Zn (wt%)? 1.8

&Quot; (2) &quot;

Si (wt%) <Al (wt%) x 0.03 + Mg (wt%) x 0.7

 &Quot; (3) &quot;

Si (wt%) <Al (wt%) x 0.03 + Mg (wt%) x 0.45

In one embodiment, the plating composition further comprises at least one metal selected from the group consisting of Zr, Cr, Sb, Ca, Sr, Be, La and Ce, and the weight of the metal is independently 0.005 to 0.2 wt% &Lt; / RTI &gt;

Specifically, the plating composition further comprises at least one selected from the group consisting of Zr and Cr, and the weight of the metal is independently 0.005 to 0.2 wt%.

Specifically, the plating composition further includes at least one selected from the group consisting of Sb, Ca, and Sr, and the weight of the metal is independently 0.005 to 0.2 wt%.

Specifically, the plating composition further includes at least one selected from the group consisting of Sr, Ca, Be, La and Ce, and the weight of the metal is independently 0.005 to 0.2 wt%.

Specifically, each of the plating compositions is composed of at least one selected from the group consisting of 0.005 to 0.2 wt% of at least one metal selected from Zr and Cr, each independently 0.005 to 0.2 wt% of at least one metal selected from Sb, Ca and Sr, And 0.005 to 0.2 wt% of at least one metal selected from Sr, Ca, Be, La and Ce.

In one embodiment, the present invention relates to a Zn-Al alloy-plated steel material excellent in corrosion resistance including a plurality of sequins uniform in size and independent on the surface of a plating layer containing the plating composition.

Specifically, the plurality of independent sequins includes an average of 10 or less floral-like Si phases having a diameter of 100 m or less per 1 mm ² of the surface of the plating layer, and more preferably the alloy- Has an average of not more than one floral-like Si phase having a diameter of 100 m or less per 1 mm ² of the surface of the plating layer.

In one embodiment, the present invention relates to an Al-Zn alloy-plated steel material having excellent corrosion resistance including a Mg ₂ Si phase of polygonal or acicular phase and an MgZn ₂ phase of irregular phase in the Zn phase region in the plating layer. The MgZn ₂ phase is formed with the Zn phase between the Al phases and is surrounded by the Zn / Al binary process or surrounded by the Zn / Al / MgZn ₂ three-phase process.

Specifically, the Mg ₂ Si phase exists mainly on the surface of the plating layer which is 10 to 20% or less of the thickness of the plating layer, the MgZn ₂ layer exists over the entire plating layer, and the plating layer contains 2 vol% or less of Mg ₂ Si phase . And the Mg ₂ Si phase contains more than 0.001 vol%. And the Mg ₂ Si phase is contained in the plating layer.

Specifically, the surface of the plating layer includes a polygonal or acicular Mg ₂ Si phase having a diameter of less than 10 μm and surrounded by a Zn / Al binary process or surrounded by a Zn / Al / MgZn ₂ three- Alloy plated steel.

In one embodiment, heating the plating composition to produce a hot-dip coating bath at 550-650 占 폚; Immersing the steel material in the plating bath for 1 to 3 seconds; Wiping with nitrogen or air to remove excess plating liquid on the steel material to which the plating liquid is adhered; And cooling to 15 to 30 占 폚 at a cooling rate of 5 to 50 占 폚 / sec. The present invention also relates to a method of manufacturing a plated steel material using the plating composition. Specifically, the present invention relates to a method for manufacturing a plated steel material having a coating amount of 60 to 200 g / m ² on the surface of a steel material by the wiping step.

The present invention relates to a method of forming an Mg ₂ Si phase (a polygonal phase or an irregular phase having a diameter of less than 10 μm) on a surface of a plating layer using an Al-Zn alloy plating composition containing Zn, Mg, Si and Al and forming a MgZn ₂ phase on the entire plating layer (Al-Zn-based alloy plated steel) having excellent corrosion resistance, workability and plating surface property by controlling the size, shape and distribution of the interstitial structure and intermetallic compound in the plating layer.

Therefore, there is a useful effect that can be widely commercialized in fields requiring excellent corrosion resistance, such as automobile, home appliance and building material field.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a micrograph of the surface of a Zn ₂ Si phase with a polygonal or acicular shape of less than 10 μm in the Zn region.
Fig. 2 is a micrograph of a plating surface and a cross-sectional electron microscope showing a Mg ₂ Si phase of a polygonal shape of 10 탆 or more.
3 is a photograph of a plating surface and a cross-section electron microscope showing a Mg ₂ Si phase in Chinese character shape.

Hereinafter, a plating composition according to the present invention, a method for manufacturing a plated steel material using the same, and a plated steel material coated with the plating composition will be described in detail.

The plating composition of the present invention is an Al-Zn based alloy plating composition comprising Zn, Mg, Si and the remainder Al.

Specifically, the plating composition comprises 35 to 55 wt% of Zn, 0.3 to 2 wt% of Mg, 0.5 to 2.5 wt% of Si, and the remainder Al based on the total weight of the composition. The above composition substantially has the composition of the plating bath or the plating layer of the plated steel.

The plating composition further comprises at least one metal selected from the group consisting of Zr and Cr. The plating composition may further include at least one metal selected from the group consisting of Sb, Ca and Sr or at least one metal selected from Sr, Ca, Be, La and Ce in the composition. (I) at least one metal selected from the group consisting of Zr and Cr, (ii) at least one metal selected from Zr and Cr, and at least one metal selected from Sb, Ca and Sr, Or iii) at least one metal selected from the group consisting of Zr and Cr, and further comprising at least one metal selected from Sr, Ca, Be, La and Ce, or vi) at least one selected from Zr and Cr And further comprises at least one metal selected from Sb, Ca and Sr, and may further comprise at least one metal selected from Sr, Ca, Be, La and Ce. The weight of the metal is independently 0.005 to 0.2 wt%. And from 40.0 to 64.2 wt% for the remainder Al.

The plating composition improves the corrosion resistance, workability and plating surface property by controlling the size and shape distribution of the interstitial structure and the intermetallic compound when forming the plating layer on the steel material.

Coating composition is a plated steel coating (alloy Al-Zn-based plated steel material) comprises a polygon phase or the needle of the Mg ₂ Si phase and amorphous on the MgZn ₂ phase in the Zn-phase region of the plating layer to improve corrosion resistance, and Mg ₂ Si phase, mainly And MgZn ₂ is present throughout the plating layer. Here, the Zn phase region refers to a region consisting of a Zn phase, a Zn / Al binary process, and a Zn / Al / MgZn ₂ three-phase process except for the dendritic Al phase and Si phase in FIG.

The Mg ₂ Si phase varies in shape and location depending on the composition. In the case of the over-processing composition in which the Mg ₂ Si phase is formed at the initial stage of solidification, the Mg ₂ Si phase has a polygonal phase mainly having a diameter of 10 μm or more and is formed independently of the Al phase of the resin. In the sub-process composition of the Al phase, the Mg ₂ Si phase is mainly formed between the Al phase of the resin phase and the Mg ₂ Si phase of the Chinese character.

In the plated steel material coated with the plating composition according to the present invention, the shape of the Mg ₂ Si phase and the occurrence position are different. In the present invention, the shape of the Mg ₂ Si phase is in the form of a polygonal or acicular shape of less than 10 μm. The generation position is present in the Zn phase region formed between the dendritic Al phases and mainly exists only in the plating surface layer portion.

The shape and position of the Mg ₂ Si phase affect the corrosion resistance and processability of the plating. That is, when forming a Mg ₂ Si phase of polygonal shape having a diameter of 10 탆 or more formed in an over-processing composition, there is no great benefit in corrosion resistance. In this case, in the early stage of corrosion, the increase of the sacrificial corrosion resistance by Mg increases the corrosion resistance in the short term exposed part of the ground iron, but the corrosion progresses with time. As shown in FIG. 2, a Mg ₂ Si phase having a polygonal shape with a diameter of 10 μm or more is scattered sporadically on the plating surface, and a Mg ₂ Si phase is formed over the entire plating thickness at the plating end. Because the Mg ₂ Si phase is sporadically formed on the plating surface, corrosion by-products also form sporadically and do not form a barrier due to corrosion by-products. The corrosion by-products thus formed are easily washed off in rainwater during the rainy season and are prone to spot redevelopment at the sites of Mg ₂ Si where the Mg is exhausted. In addition, a polygonal Mg ₂ Si phase having a diameter of 10 탆 or more provides a site where a crack occurs during processing due to a difference in physical properties between the plating layer and the base layer. The Mg ₂ Si phase of Chinese character formed in the sub-process composition of the Al phase and the process structure also has no great benefit in corrosion resistance and processability. The Mg ₂ Si phase of the Chinese character is distributed more densely than the Mg ₂ Si phase of the polygonal diameter of 10 ㎛ or more, so that the corrosion effect by the Mg ₂ Si phase is further maintained. Is the same. As shown in FIG. 3, when the amount of the plating is small, the Mg ₂ Si phase of the Chinese character is formed over the entire plating, and after the Mg is exhausted, the corrosion rate is accelerated by providing the corrosion path together with the Zn phase. This is the same principle that the Zn phase region in the bamboo structure, which is common in Al-Zn plating, provides a corrosion path and lowers the corrosion resistance when the plating amount is small or the cooling rate is small. In addition, the Mg ₂ Si phase in the Chinese character shape provides a path through which cracks generated during machining can be propagated, resulting in a lower machinability than a plating having a Mg ₂ Si phase of a polygonal shape having a diameter of 10 μm or more.

Accordingly, the Mg ₂ Si phase formed in the present invention is present in the Zn phase region formed between the Al phase of the resin in the form of a polygonal phase or an acicular phase of less than 10 탆 in diameter, thereby improving the corrosion resistance and workability. In general, the Al-Zn coated steel sheet has a resistance to corrosion while the dendritic Al phase forms a whole skeleton of the plating, and the Zn phase region formed between the dendritic Al phases acts as a sacrificial method and has improved corrosion resistance . However, the corrosion resistance is still insufficient in the cuts exposed to iron oxide. Therefore, the Mg ₂ Si phase formed in the present invention is uniformly dispersed in the Zn phase region in the form of a polygonal phase or a needle-like phase having a diameter of less than 10 탆, and the Mg ₂ Si phase having a diameter of 10 탆 or more and the Mg ₂ Si And the sacrificial corrosion resistance of the Zn phase region is increased, thereby improving the corrosion resistance of the cut portion where the base iron is exposed. In particular, even if a bamboo structure is formed due to a small plating amount or a slow cooling rate, the corrosion rate is delayed due to the Mg ₂ Si phase formed in the Zn phase region, thereby improving the corrosion resistance to the surface. Since the Mg ₂ Si phase formed in the present invention is not so large as less than 10 μm in diameter and is formed in the Zn phase region in the form of a polygonal phase or an acicular phase, it does not act as a crack propagation path or acts as a crack propagation pathway, do.

The Al-Zn based alloy plating using the plating composition starts to solidify at 530 to 580 캜 and finishes at about 325 to 335 캜. The type, shape and order of the phases formed in this process are affected by Mg content, Si content, and Zn content.

In the range of the plating composition of the present invention, the Al phase is formed as a primary phase in the solidification process to form a dendritic phase, and the Si phase starts to form when the solidification temperature is near 500 캜. In the remaining liquid phase, the Mg ₂ Si phase is formed as a polygonal phase or a needle-like phase having a diameter of less than 10 μm while being formed first. Subsequently, the atypical MgZn ₂ phase coagulates with the Zn / Al binary process or the Zn / Al / MgZn ₂ binary process to form the Zn phase. Here, the Al phase is Al solid solution containing Zn in a solid solution containing a small amount of Mg.

In order to form sequins with a large number of independent sequins, that is, a sequins having clearly defined sequins (the boundaries between sequins and sequins are clearly distinguished), it is necessary to include not more than 10 floral-shaped Si phases with a diameter of 100 μm or less per 1 mm ² Or less. The number of the floral patterned Si phase having a diameter of 100 m or less per 1 mm ^{2 of the} surface of the plating surface is 10 or less when the formula Si (wt%) <Al (wt%) x 0.03 + Mg (wt%) x 0.7 is satisfied, (Wt%) < Al (wt%) x 0.03 + Mg (wt%) x 0.45. The above formulas are relational expressions for improving the surface property and workability by minimizing the precipitation of the Si phase on the surface of the plating layer and the inside due to the excess Si. The above formula is a result of calculating the optimum weight of Si, Al, and Mg depending on the formation of the sequins through repeated experiments with different weights of Si, Al and Mg.

If the Si content is more excessive than the amount of Si used in the control of the alloy layer thickness and the Mg ₂ Si phase formation, the excess amount forms needle-like needle-like Si phase between the plating layers, which leads to poor workability. In addition, during the solidification process of the plating layer, excessive Si is concentrated on the surface and formed, thereby preventing formation of a sequin which is an outward characteristic of the Al-Zn alloy-plated steel sheet and deteriorating the surface properties of the plating.

Hereinafter, reasons for limiting the function and content of the constituent elements of the plating composition of the present invention will be described.

Zn: 35 to 55 wt%

Zn dissolves preferentially to Fe, which is a brittle iron, to retard Fe corrosion. This is called sacrificial antimicrobial property, and the sacrificial antimicrobial property is ensured at a content of Zn of 35 wt% or more with respect to the total weight of the composition. If the content of Zn is less than 35 wt%, the corrosion resistance of the cut surface is deteriorated. On the other hand, if the content of Zn exceeds 55 wt% with respect to the total weight of the composition, the sacrificial corrosion resistance gradually increases but not so much, and the Al ₂ O ₃ coating formed on the plating surface due to the Al component can not be densely formed, The basic corrosion resistance of the alloy plating is reduced. Also, when the content of Zn exceeds 55 wt%, the increase of the specific gravity of the whole composition is insufficient for the cost.

The ratio of Al (wt%) / Zn (wt%) is preferably 0.9 to 1.8 in order to ensure a beautiful surface appearance and corrosion resistance. If the ratio of Al (wt%) / Zn (wt%) is less than 0.9 or exceeds 1.8, the sequins are not clear or the corrosion resistance is poor.

Mg: 0.3 to 2 wt%

Mg is an important element for improving corrosion resistance. Mg is further improved the corrosion resistance of the Al-Zn alloy-plated steel material by covering the exposed surface of the plating layer and the exposed portion of the substrate with corrosion products when the coated steel coated with the Al-Zn based alloy coating composition is exposed to the corrosive environment .

Mg in the plating layer is combined with Si and Zn to form an intermetallic compound Mg ₂ Si phase and MgZn ₂ phase. The Mg ₂ Si phase and the MgZn ₂ phase accelerate the formation of stable corrosion products in the corrosive environment and become a source of the Mg component. As a result, the surface of the plated layer is quickly covered with a uniform corrosion product. This corrosion product acts as a stable protective film and improves the corrosion resistance of the plating layer.

Mg is also involved in the sacrificial corrosion resistance of the plated steel together with Zn. Mg is involved in sacrificial anchoring in that the sacrificial action is kept long.

In addition, Mg reacts with Al to block the diffusion of oxygen, thereby significantly improving the corrosion resistance on the front surface after machining.

In addition, Mg exists as an oxide in the extreme surface layer of the plating layer, contributing to improvement in corrosion resistance, and the effect of improving the corrosion resistance is large even when the content is very small.

In order to form the Mg ₂ Si phase, Mg should be added in an amount of 0.3 wt% or more based on the total weight of the composition. Preferably, the amount of Mg added is 0.5 wt% or more. In order to form an acicular or polygonal Mg ₂ Si phase of less than 10 μm in the Zn phase region of the plating layer, it should not exceed 2 wt%. Mg content, this amount on the Mg ₂ Si below 2wt% is taken to 2vol% or less in the entire plating layer wherein Al is not between the different Chinese Mg ₂ Si in the character shape is formed between, under 10㎛ polygon in a region Zn Phase or needle-like Mg ₂ Si phase. On the other hand, if the amount of Mg added exceeds 2 wt%, Mg oxide is easily generated during plating, and defects due to Mg oxide are likely to occur on the surface of the plating. Preferably, the amount of Mg added is 1 wt% or less. When the amount of Mg added is less than 1 wt%, it is possible to use the non-100% nitrogen air in the wiping step for controlling the amount of plating, which is advantageous in terms of cost.

Si: 0.5 to 3 wt%

Si is added in order to suppress the growth of Fe-Al-based alloy layer formed on the base iron and the interface, and to improve the fluidity of the plating bath to give gloss. When the production of the Fe-Al-based alloy layer is suppressed, the workability is improved.

The addition of Si forms a Mg ₂ Si phase containing Mg. This image is effective for improving the corrosion resistance of the front end face of the plating layer and the processed portion.

Si is added in an amount of 0.5 wt% or more based on the total weight of the composition, the above-mentioned effect can be expected. However, when added in an amount exceeding 3 wt%, needle-like Si needles precipitate in the plating layer, resulting in remarkable deterioration in workability and excess Si is concentrated on the surface to form a sequin which is an extrinsic characteristic of the Al-Zn alloy- Thereby deteriorating the surface properties of the plating.

The Al-Zn-based alloy plating composition may contain one or more metals selected from Zr and Cr or one or more metals selected from among Sb, Ca and Sr or one or more metals selected from Sr, Ca, Be, La and Ce, or Zr And Cr, and at least one metal selected from among Sb, Ca, and Sr, and at least one metal selected from among Sr, Ca, Be, La, and Ce. The weight of the metal is independently 0.005 to 0.2 wt%.

Zr and Cr can be added to further improve the corrosion resistance of the Al-Zn based alloy plating. Zr additionally improves Mg intermetallic compound and Zn phase sacrificial corrosion resistance, and Cr improves corrosion resistance of Al phase to improve corrosion resistance.

Sb, Ca and Sr can be added to improve the workability by controlling the shape and size of the Mg ₂ Si phase. Sb, Ca and Sr can be miniaturized to the size acts as a nucleation site on the Mg ₂ Si, or Al-Zn-based alloy improves the workability of the coating by inhibiting the formation of Mg ₂ Si in the Chinese character shape.

Sr, Ca, Be, La, and Ce can be added to improve the surface properties and workability of the Al-Zn based alloy plating. In the Al-Zn based alloy plating composition, the surface of the molten metal is easily covered with the Mg oxide due to the addition of Mg, so that defects due to adsorption of Mg oxide are likely to occur during the plating operation. Sr, Ca, Be, La, and Ce are oxidized prior to Mg, and dense oxides are formed on the surface of the plating bath while oxides formation by Mg is suppressed.

At least one selected from among Zr, Cr, Sb, Ca, Sr, Ca, Be, La and Ce is added in an amount of 0.005 wt% or more. On the other hand, when the amount exceeds 0.2 wt%, a large amount of dross is generated in the plating bath, thereby causing a problem of impairing the appearance of the plating surface due to the adsorption of dross.

When at least one metal selected from Zr or Cr and at least one metal selected from Sb, Ca and Sr and at least one metal selected from Sr, Ca, Be, La and Ce are simultaneously added, corrosion resistance, workability, And the workability improving effect is further increased.

The plating composition of the present invention contains the above components, and the balance is Al. Such a plating composition is an element contained depending on the conditions of raw materials, materials, manufacturing facilities and the like, and fine admixture of unavoidable impurities of 0.001 wt% or less is also permitted. Particularly in the case of Fe, it is possible to incorporate up to 0.5 wt% from the manufacturing facility or the steel to be plated.

The present invention also provides a method for forming an Al-Zn based alloy plating layer by coating a steel material with the plating composition of the present invention.

A method for coating a plating composition on a steel material comprises the steps of: heating a plating composition having the above composition to prepare a hot-dip coating bath at 550 to 650 DEG C; and dipping the steel material in a plating bath to cover the surface of the plating composition, And cooling to room temperature at a cooling rate of 50 DEG C / sec.

The steel may be a cold-rolled steel sheet or a hot-rolled steel sheet or a steel sheet annealed after cold-rolling. Then, the steel material is adjusted to the plating bath temperature before being immersed in the plating bath, and then immersed in the plating bath. After the steel material is immersed in the plating bath, it is lifted up and the amount of plating adhered by air or nitrogen is adjusted by air wiper. If necessary, it can pass through a mini-sequin chamber or a galvanic annealing furnace. At this time, the plating adhesion amount is adjusted to be 60 to 200 g / m ² . If the temperature of the plating bath molten metal is less than 550 ° C, the fluidity of the plating bath is deteriorated and the appearance of the plating film becomes poor and the plating adhesion is lowered. On the other hand, when the temperature exceeds 650 ° C, the amount of Fe elution from the plating bath molten steel bath increases, thereby increasing the amount of dross generated and causing insufficient cooling in the solidification process after plating, thereby generating defects such as a flow mark on the plating layer.

If the cooling rate is less than 5 ° C / sec, a large amount of Si phase is formed on the surface of the plating, and the formation of the sequins, which is an outward characteristic of the Al-Zn alloy coated steel sheet, is inhibited and the surface properties of the plating are deteriorated. On the other hand, if the cooling rate exceeds 50 ° C / sec, there arises a problem that the surface of the plating layer becomes rough due to overcooling and the Mg ₂ Si phase is not formed.

The cooling rate not only controls the size and shape of the Mg ₂ Si phase, but also affects the development of dense plating tissue. When the cooling rate is in the range of 15 to 35 ° C./sec, the dendrite structure is well developed on the plating surface and the dendrite arm spacing is small, the number of layers of the Al layer is increased in the plating section structure It has a complicated corrosion path, and the corrosion resistance is further improved. Therefore, the cooling rate is more preferably in the range of 15 to 35 DEG C / sec.

When the coating amount is less than 60 g / m ^{2, the} corrosion resistance is insufficient. When the coating amount exceeds 200 g / m ² , the coating layer becomes excessively thick due to the excessive coating amount, so that the adhesion of the coating layer itself decreases and the surface gloss decreases.

Immersion is carried out for 1 to 3 seconds. If the immersion is less than 1 second, the adhesion of the plating becomes low, and if it exceeds 3 seconds, the alloy layer becomes thick in the plating layer, and the workability may be deteriorated.

As described above, the plating composition is coated to form an Al-Zn based alloy plating layer on the surface of the steel, and the Mg ₂ Si phase and the MgZn ₂ phase are contained in the plating layer.

The plating layer is a structure in which the Mg ₂ Si phase and the MgZn ₂ phase are mixed with the Al phase, Zn phase, Al / Zn binary process phase and Al / Zn / MgZn ₂ three-phase process phase.

Specifically, a Mg ₂ Si phase and a MgZn ₂ phase are contained in the plating layer, and a plurality of independent sequins are formed on the surface of the plating layer. Multiple independent sequins are uniform in size and clearly distinguish between sequins and sequins.

The Mg ₂ Si phase is mainly distributed on the surface of the plating layer and is surrounded by a Zn / Al binary process in the Zn phase region of the plating layer or surrounded by a Zn / Al / MgZn ₂ three-phase process and formed into a polygonal or acicular shape with a diameter of less than 10 μm do.

The MgZn ₂ phase is formed with the Zn phase between the Al phases and is surrounded by the Zn / Al binary process or surrounded by the Zn / Al / MgZn ₂ binary process.

It is also possible to form a plurality of independent sequins including an average of not more than 10 flower-shaped Si phases having a diameter of 100 m or less per 1 mm ² of the surface of the plating layer, or a flower-shaped Si phase having a diameter of 100 m or less per 1 mm ² of the surface of the plating layer On the average of one or less to form a plurality of independent sequins.

Hereinafter, the present invention will be described in detail with reference to comparative examples different from the examples. However, the following examples are illustrative of the present invention, and the present invention is not limited by the following examples.

[Example 1]

Manufacture of plated steel

Prepare the cold rolled steel sheet with thickness, width, and length of 1.2 mm, 180 mm, and 220 mm, respectively, by immersing the cold rolled steel sheet in 50 ° C alkaline solution for 30 minutes and then rinsing with water to remove foreign substances and oil from the surface.

This specimen is annealed and then plated. The annealing is performed in a reducing atmosphere composed of 10 to 30% of hydrogen and 70 to 90% of nitrogen, and the annealing temperature is 750 to 850 ° C. Here, the annealing is carried out in a reducing atmosphere to prevent Al because Al has a strong affinity with Fe and reactivity with oxygen is high and it is easy to form a dotted platelet.

The plating was performed by cooling the specimens subjected to the annealing heat treatment to a plating bath temperature, immersing them in the plating bath for 2 seconds, pulling them up, adjusting the coating amount to 60 to 200 g / m ² by using an air wiper using nitrogen, sec to a room temperature to coagulate. The plating bath temperature is 550 to 650 ° C.

[Table 1] (Unit: wt%)

Table 1 shows the plating bath composition and composition ratio of the inventive example and comparative example.

[Example 2]

Plating the specimen with a plating bath and evaluation of physical properties

[Table 2]

Table 2 shows the results of analyzing the texture of the plated steel material produced in Example 1 and evaluating the physical properties thereof.

1) Evaluation of plating surface property

The clarity of the sequins on the surface of the plating according to the plating composition and whether or not the plating was formed were visually observed.

◎: Consistent sequin formation and almost no surface defects

○: Consistent sequin formation

△: Sequins are formed but not distinct

X: No sequins formed

In Comparative Example 3 and Comparative Example 4, a sequins were formed, but the boundaries between the sequins and the sequins were not clear.

Comparative Example 3 did not satisfy the condition that the ratio of Al (wt%) / Zn (wt%) was 0.9 to 1.8 and Comparative Example 4 did not satisfy the relation Si (wt%) <Al (wt%) x 0.03 + Mg (wt% ) × 0.7, and it seems that there is a difference depending on the degree.

On the other hand, Comparative Examples 1 and 2, Comparative Example 5, and Inventive Examples 1 to 3, which satisfied the above conditions, formed sequins having distinct shapes.

Examples 4 to 8 containing at least one selected from among Sr, Ca, Be, La, and Ce exhibited the most favorable plating surface properties because of no formation of defects together with formation of sequins having distinct shapes.

2) Evaluation of processability

The specimen was bent 180 degrees to a thickness of 1 T (bending test), and the cross-section was observed with a microscope to measure the cracking rate per unit length. At this time, the crack is limited only to the entire plating layer.

◎: Crack occurrence rate 10% or less

○: Cracking rate exceeding 10% and not more than 20%

C: Cracking rate exceeding 20% and not more than 30%

X: More than 30% crack occurrence rate

In Comparative Example 2, the cracking rate exceeded 30%. The comparative example 2 satisfies the condition Si (wt%) <Al (wt%) x 0.03 + Mg (wt%) x 0.7 but the sub-process composition in which the vol% of the Mg ₂ Si phase is 2% Since Mg ₂ Si phase was formed, the workability was the weakest.

In Comparative Examples 1 and 4, the cracking rate was more than 20% and 30% or less.

Comparative Example 1 is the condition Si (wt%) <Al ( wt%) × 0.03 + Mg (wt%) satisfy the one or more ㅧ 0.7 10㎛ a eutectic composition and that of the Primary Mg ₂ Si phase Mg ₂ Si phase to form polygon on the was formed in Comparative example 4 does not satisfy the phase of less than 10㎛ polygonal or needle of Mg ₂ Si to form a one-phase condition Si (wt%) <Al ( wt%) × 0.03 + Mg (wt%) × 0.7 a large amount of Since the needle-shaped Si phase was formed, the workability was weakened.

Comparative Example 3 which forms a polygonal or needle-like Mg ₂ Si phase satisfying the condition Si (wt%) <Al (wt%) x 0.03 + Mg (wt%) x 0.7 and less than 10 μm and Comparative Examples 3 and 4 And Examples 6 to 7 all exhibited superior workability to Comparative Example 1. [

Examples 3 to 5 and at least one of Inventive Example 8 in which at least one selected from Sb, Ca, and Sr were included had improved processability before the addition of these elements and Comparative Example 5 in which no Mg ₂ Si phase was produced, And the same level of workability.

3) Evaluation of planar corrosion resistance

In accordance with KS D 9502 (ASTM B-117), rust development was evaluated by a salt spray test at 5% NaCl and 4000 hours at 35 ° C.

The surface of the specimen was coated on all four sides, and after 4000 hours, the surface of the specimen was visually observed to observe the occurrence of redness. At this time, specimens having a plating thickness of 10 to 12 μm were used.

⊚: Red rust occurrence rate of 5% or less

○: Red rust occurrence rate exceeding 5% and below 10%

?: Red rust occurrence rate exceeding 10% and not more than 30%

×: Red rust occurrence rate exceeding 30%

Comparative Example 3 did not satisfy the condition that the ratio of Al (wt%) / Zn (wt%) was 0.9 to 1.8, showing the most heat resistance. Mg ₂ Si phase or on the more 10㎛ polygon are compared Chinese character form of Mg ₂ Comparative Examples 1 to 2 and Mg ₂ Si phase is generated Si phase formed Comparative Example 5 is lower than the 10㎛ polygonal or needle of the Mg ₂ Si phase is formed Example 4 and Examples 1 and 8 showed corrosion resistance against heat.

And Examples 2 to 7 including at least one selected from Zr and Cr improved the corrosion resistance before the addition of these elements.

[Example 3]

Evaluation of the physical properties of the plating layer according to the plating bath temperature (the temperature of the molten bath of the plating bath) and the cooling rate after coating the plating composition

The composition of the plating composition for forming the plating bath includes 41.5 wt% of Zn, 1.5 wt% of Mg, 2 wt% of Si, and the balance of Al and impurities. Then, the steel material is adjusted to the plating bath temperature before being immersed in the plating bath, and then immersed in the plating bath.

Table 3 below shows evaluation of physical properties according to plating bath temperature and cooling rate.

 [Table 3]

1) Evaluation of plating surface property

The degree of unevenness on the plating surface according to the plating bath temperature was visually observed.

○: Beautiful

△: Smear generation such as surface flow marks

X: Defective appearance due to severe dirt, lowering surface gloss

2) Evaluation of processability

The specimen was bent 180 degrees to a thickness of 1 T (bending test), and the cross-section was observed with a microscope to measure the cracking rate per unit length. At this time, the crack is limited only to the entire plating layer.

◎: Crack occurrence rate 10% or less

○: Cracking rate exceeding 10% and not more than 20%

C: Cracking rate exceeding 20% and not more than 30%

X: More than 30% crack occurrence rate

2-1) Plating bath temperature

When the plating bath temperature is lower than 550 占 폚, the appearance of the plating surface is poor and the workability is deteriorated. This seems to be due to the deterioration of the plating bath fluidity. When the plating bath temperature exceeded 650 캜, unevenness like a flow mark occurred in the plating layer.

2-2) Cooling speed

When the cooling rate after plating was less than 5 ° C / sec, a large amount of Si phase was formed on the surface of the plating, and the formation of the sequins was blocked to deteriorate the surface properties of the plating. When the cooling rate exceeds 50 DEG C / sec, the surface gloss is lowered. Particularly, when the cooling rate is 15 to 35 DEG C / sec, corrosion resistance and workability are improved.

As a result of the above-described experimental results, the plating is performed so that the Mg ₂ Si phase is formed in the plating layer by the Al-Zn alloy plating composition containing Zn, Mg, Si and the remainder Al, (Al-Zn alloy-plated steel) excellent in corrosion resistance, workability, and plating surface property can be manufactured by controlling the size and shape of the intermetallic compound.

It will be understood by those skilled in the art that various changes and modifications may be made without departing from the scope of the present invention.

10: phase Mg ₂ Si on the under 10㎛ polygon 20: a needle under 10㎛ Mg ₂ Si phase
30: Al phase 40: Zn phase
50: Zn / Al binary process 60: Zn / Al / MgZn ₂ process
70: MgZn ₂ phase 80: Polygonal Mg ₂ Si phase
90: Mg ₂ Si phase in Chinese character shape

Claims (11)

With respect to the total weight of the plating composition,
35 to 55 wt% of Zn, 0.3 to 2 wt% of Mg, 0.5 to 3 wt% of Si, and the balance Al,
Wherein the plating composition satisfies the following conditions (1) and (2).
[Equation 1]
0.9? Al (wt%) / Zn (wt%)? 1.8
&Quot; (2) &quot;
Si (wt%) <Al (wt%) x 0.03 + Mg (wt%) x 0.7
The method according to claim 1,
Wherein the plating composition satisfies the following formula (3).
&Quot; (3) &quot;
Si (wt%) <Al (wt%) x 0.03 + Mg (wt%) x 0.45
The method according to claim 1,
Wherein the plating composition further comprises at least one metal selected from Zr, Cr, Sb, Ca, Sr, Be, La, and Ce,
Wherein the weight of the metal is independently 0.005 to 0.2 wt%.
An Al-Zn alloy-plated steel material excellent in corrosion resistance comprising a sequin formed on the surface of a plating layer comprising the plating composition of any one of claims 1 to 3.
5. The method of claim 4,
The sequin has an average of 10 or less Si phases having a diameter of 100 m or less per 1 mm ² of the surface of the plating layer, and has an excellent corrosion resistance.
5. The method of claim 4,
Wherein the sequins include an average of not more than 1 Si phase having a diameter of not more than 100 mu m per 1 mm ² of the surface of the plating layer.
5. The method of claim 4,
Wherein the plating layer contains a Mg ₂ Si phase of a polygonal or acicular phase and a MgZn ₂ phase of an irregular phase within a Zn phase region, and is excellent in corrosion resistance.
8. The method of claim 7,
The Mg ₂ Si phase exists in a plating surface portion of 10 to 20% or less of the total thickness of the plating, and the MgZn ₂ is present throughout the plating layer and is excellent in corrosion resistance.
5. The method of claim 4,
And the plating layer contains 2 vol% or less of Mg ₂ Si phase.
5. The method of claim 4,
And a polygonal or acicular Mg ₂ Si phase formed on the surface of the plating layer and having a diameter of less than 10 μm and surrounded by a Zn / Al binary process or surrounded by a Zn / Al / MgZn ₂ three- Al-Zn alloy-plated steel.
A method for producing a hot-dip galvanizing bath, comprising: heating a plating composition according to any one of claims 1 to 4 to produce a hot-dip coating bath at 550 to 650 ° C;
Immersing the steel material in the plating bath for 1 to 3 seconds;
Plating with a coating amount of 60 to 200 g / m ² on the surface of the steel material by wiping with nitrogen or air to remove excess plating solution on the steel material with the plating solution attached thereto; And
And cooling the steel sheet at a cooling rate of 5 to 50 占 폚 / sec to 15 to 30 占 폚.

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