WO2016093667A1 - Plating composition, method for manufacturing plated steel material by using same, and plated steel material coated with plating composition - Google Patents

Abstract

The present invention relates to a plating composition, a method for manufacturing a plated steel material by using the same, and the plated steel material coated with the plating composition, the composition containing, based on the total weight of the plating composition, 35-55 wt% of Zn, 0.3-2 wt% of Mg, 0.5-3 wt% of Si, and the remainder being Al, wherein the plating composition satisfies mathematical formula 1, 0.9≤Al(wt%)/Zn(wt%)≤1.8 and mathematical formula 2, Si(wt%)<Al(wt%)x0.03+Mg(wt%)×0.7. The present invention controls the internal microstructure of the plating layer and the size and shape of intermetallic compounds, thereby manufacturing the plated steel material (Al-Zn-based alloy plated steel material) having excellent corrosion resistance, workability and plated surface properties.

Description

Plating composition, method of manufacturing plated steel using the same and plated steel coated with plating composition

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

Galvanized steel sheet using zinc, which has a higher tendency to ionize than iron, has been used for a long time because of its excellent corrosion resistance to prevent corrosion of iron. Galvanized steel is now widely used in the fields of automobiles, appliances and building materials.

However, galvanized steel sheet used in the field of building materials is increasing the demand for improved corrosion resistance as the level of consumer desire increases.

In the late 1960s, Al-Zn-coated steel sheets, called galvalumes, were developed and used as corrosion-resistant plated steel sheets for building materials. However, Al-Zn plated steel sheet has excellent corrosion resistance compared to the conventional galvanized steel sheet, but the problem was found to be poor in corrosion resistance in the cut exposed steel.

Prior arts related to this include Korean Patent Registration No. 10-1091341 (2011.12.07) _ "Steel coating composition and zinc or zinc-based alloy plate steel sheet excellent in workability, adhesiveness, weldability and alkali film removal property".

An object of the present invention is to provide a plating composition, a method for producing a plated steel using the same, and a plated steel coated with the plating composition.

Specifically, in order to solve the above-described problems, with respect to the total weight of the plating composition, Zn 35 ~ 55wt%, Mg 0.3 ~ 2wt%, Si 0.5 ~ 3wt% and the balance Al, the plating composition is represented by the following equation 1 and An object of the present invention is to provide a plating composition that satisfies the condition of Equation 2.

[Equation 1]

0.9 ≤ Al (wt%) / Zn (wt%) ≤ 1.8

[Equation 2]

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

 In addition, the present invention is to provide a plating composition, a method of manufacturing a plated steel material using the same and a plated steel plate coated with the coating composition, which is effective in improving corrosion resistance and also ensures workability and excellent plating surface properties.

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

For a thorough understanding of the present invention, various specific details are described, such as specific forms, compositions, processes and the like. However, certain embodiments may be practiced without one or more of these specific details, or in conjunction with other known methods and forms. In other instances, well known processes and manufacturing techniques have not been described in particular detail in order to not 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 one or more embodiments of the invention. Thus, the context of the expression “in one embodiment” or “embodiment” in various places throughout this specification does not necessarily represent the same embodiment of the invention. In addition, particular features, forms, compositions, or properties may be combined in any suitable manner in one or more embodiments.

In the present invention, the polygonal shape refers to a figure surrounded by three or more line segments, for example, a triangle, a square, a pentagon, or a hexagon, which is not limited to the examples.

In the present invention, the Chinese character means the Mg ₂ Si phase formed in the plating layer as shown in FIG. The Chinese character is the Mg ₂ Si phase formed when forming the process structure together with the Al phase in the subprocess composition.

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

Specifically, the plating composition is a plating composition that satisfies the conditions of the following equations (1) and (2), and more preferably relates to a plating composition that satisfies the condition of the following equation (3). Equations 1 to 3 below derive a relationship between the weights of Si, Al, and Mg through a plurality of embodiments, as in the embodiment of the present invention.

[Equation 1]

0.9≤Al (wt%) / Zn (wt%) ≤1.8

[Equation 2]

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

 [Equation 3]

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

In one embodiment, the plating composition further comprises at least one metal selected from Zr, Cr, Sb, Ca, Sr, Be, La and Ce, the weight of the metals are each independently 0.005 ~ 0.2wt% It relates to a plating composition included.

Specifically, the plating composition further comprises at least one metal selected from Zr or Cr, and the weight of the metal is independently related to the plating composition is contained in 0.005 ~ 0.2wt%.

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

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

Specifically, the plating composition is each independently at least one metal selected from 0.005 to 0.2wt% Zr or Cr, each independently 0.005 to 0.2wt% of at least one metal selected from Sb, Ca and Sr and each independently It relates to a plating composition further comprising at least one metal selected from 0.005 to 0.2 wt% of Sr, Ca, Be, La, and Ce.

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

Specifically, the plurality of independent sequins relates to an alloy plating steel formed by including an average of 10 or less floral pattern Si phase having a diameter of 100 μm or less per 1 mm ² area of the plating layer, more preferably the independent multiple The sequin of relates to an alloy plated steel material comprising, on average, one or less floral pattern Si phases having a diameter of 100 µm or less per 1 mm ² surface area of the plating layer.

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

Specifically, the Mg ₂ Si phase is mainly present in the 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, the plating layer containing 2% or less of Mg ₂ Si phase It features. The Mg ₂ Si phase is characterized in that it comprises more than 0.001vol%. Characterized in that the coating layer containing the Mg ₂ Si phase.

Specifically, the surface of the plating layer having a diameter of less than 10㎛, including a polygonal or needle-like Mg ₂ Si phase formed by being surrounded by a Zn / Al binary process or surrounded by a Zn / Al / MgZn ₂ ternary process An alloy plating steel material.

In one embodiment, heating the plating composition to prepare a hot-dip plating bath of 550 ~ 650 ℃; Immersing the steel in the plating bath for 1 to 3 seconds; Wiping with nitrogen or air to remove excess plating liquid on the steel to which the plating liquid is attached; And it relates to a method for producing a plated steel using a plating composition comprising the step of cooling to 15 to 30 ℃ at a cooling rate of 5 ~ 50 ℃ / sec. Specifically, the method of manufacturing a plated steel having a plating adhesion amount of 60 to 200 g / m ² on the surface of the steel by the wiping step.

The present invention is an Al-Zn-based alloy plating composition containing Zn, Mg, Si and the balance Al to form a Mg ₂ Si phase (polygonal or needle shape with a diameter of less than 10㎛) on the plating surface and MgZn ₂ phase is formed over the entire plating layer Plating is performed to control the size, shape, and distribution of the structure and the intermetallic compound in the plating layer to produce a plated steel (Al-Zn-based alloy plated steel) excellent in corrosion resistance, processability and plating surface properties.

Therefore, there is a useful effect that can be widely commercialized in the field requiring excellent corrosion resistance, such as automotive, home appliances and building materials.

1 is a plated surface electron micrograph showing a polygonal or needle-like Mg ₂ Si phase of less than 10 μm in the Zn region.

2 is a plated surface and a cross-sectional electron micrograph showing a polygonal Mg ₂ Si phase of 10 µm or more.

Figure 3 is a plated surface and a cross-sectional electron micrograph showing the Chinese character Mg ₂ Si phase.

Polygonal Mg ₂ Si Phase of less than 10:10 μm 20: Needle Mg ₂ Si Phase of less than 10 μm

30: Al phase 40: Zn phase

50: Zn / Al Binary Phase 60: Zn / Al / MgZn ₂ Binary Phase

70: MgZn ₂ phase 80: Mg ₂ Si phase of 10 µm or more polygonal phase

90: Mg ₂ Si phase of Chinese character

The present invention, Zn 35 ~ 55wt%, Mg 0.3 ~ 2wt%, Si 0.5 ~ 3wt% and the balance Al relative to the total weight of the plating composition, the plating composition satisfies the conditions of the following equations (1) and (2) It relates to a plating composition.

[Equation 1]

0.9 ≤ Al (wt%) / Zn (wt%) ≤ 1.8

[Equation 2]

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

Hereinafter, a plating composition according to the present invention, a method of manufacturing a plated steel using the same, and a plated steel 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, which comprises Zn, Mg, Si, and the balance Al.

Specifically, the plating composition includes Zn: 35 to 55 wt%, Mg: 0.3 to 2 wt%, Si: 0.5 to 2.5 wt%, and the balance Al based on the total weight of the composition. The composition is substantially the same as the composition of the plating bath and the plating layer of the plated steel.

The plating composition further comprises at least one metal selected from Zr or Cr. In addition, the plating composition may further include at least one metal selected from Sb, Ca, and Sr or at least one metal selected from Sr, Ca, Be, La, and Ce in the composition. That is, i) further comprising at least one metal selected from Zr or Cr in the plating composition, or i) further comprising at least one metal selected from Zr or Cr, and at least one metal selected from Sb, Ca and Sr. Or further comprising at least one metal selected from Zr or Cr, further comprising at least one metal selected from Sr, Ca, Be, La, and Ce, or at least one selected from Zr or Cr. Further comprising a metal, and further comprising at least one metal selected from Sb, Ca and Sr, may further comprise at least one metal selected from Sr, Ca, Be, La and Ce. The weight of the metal is independently included in 0.005 ~ 0.2wt%. The balance Al is included in the range of 40.0 ~ 64.2wt%.

The plating composition controls the size and shape distribution of the structure and the intermetallic compound in the plating layer when forming the plating layer on the steel to improve the corrosion resistance, processability and plating surface properties.

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 present in the plating surface portion and MgZn ₂ are present throughout the coating layer. Here, the Zn phase region refers to a region composed of a Zn phase, a Zn / Al binary process, and a Zn / Al / MgZn ₂ ternary process phase except for the Al and Si phases of the resin phase in FIG. 1.

The Mg ₂ Si phase has a shape and a generation position depending on the composition. In the case of the over-process composition in which the Mg ₂ Si phase is formed by solidification upon solidification, the Mg ₂ Si phase has a polygonal phase of 10 µm or more in diameter and is formed independently of the Al phase of the resin phase. For O eutectic composition forms a step tissue with the Al, Mg ₂ Si phase mainly having the Mg ₂ Si phase Chinese character shape is formed in between the dendrites of Al.

In the plated steel coated with the plating composition according to the present invention, there is a difference in the shape and the generation position of the above-mentioned Mg ₂ Si phase. The shape of the Mg ₂ Si phase in the present invention has a polygonal shape or needle shape of less than 10㎛. The generation position exists in the Zn phase region formed between the Al phase of the resin phase and mainly exists only in the plating surface layer portion.

The shape and location of the Mg ₂ Si phase affect the corrosion resistance and workability of the plating. That is, in the case of forming a polygonal Mg ₂ Si phase having a diameter of 10 μm or more formed in an over-process composition, there is no great benefit in corrosion resistance. In this case, the corrosion resistance is improved in the short term in the cut portion exposed to the ferrous iron due to the increase of the sacrificial corrosion resistance by Mg in the early stage of corrosion, but the corrosion proceeds rapidly as time passes. Since the diameter is distributed sporadically in the Mg ₂ Si phase plating on the surface over 10㎛ polygons as in Figure 2, the plating section is Mg ₂ Si phase is formed over the entire coating thickness. Since the Mg ₂ Si phase is sporadically formed on the plating surface, the corrosion by-products are also sporadically formed and do not form a barrier by the corrosion by-products. Corrosion by-products thus formed are easily washed off in rainwater during the rainy season, such as rainy season, and reddish red and red on the Mg ₂ Si phase where Mg is exhausted easily occurs. In addition, the polygonal Mg ₂ Si phase of 10㎛ or more in diameter provides a site (site) where cracks occur during processing due to the difference in physical properties with the base layer of the plating. The Chinese character Mg ₂ Si phase formed from the sub-process composition forming the process structure together with the Al phase also has no great benefit in corrosion resistance and workability. If on the Mg ₂ Si Chinese character form, it is less densely distributed than the Mg ₂ Si on the least diameter 10㎛ polygon progress of corrosion rapidly as the only time that the system effects of the Mg ₂ Si to be kept more elapsed The phenomenon is the same. When the amount of plating adhesion is small, as shown in Figure 3, the Chinese character Mg ₂ Si phase is formed throughout the plating and after Mg is exhausted, it provides a corrosion path along with the Zn phase to accelerate the corrosion rate. This is the same principle that the Zn phase region in the bamboo structure, which is common in Al-Zn plating when the plating adhesion amount is small or the cooling rate is small, inferior in corrosion resistance while providing a corrosion path. In addition, the Chinese character Mg ₂ Si phase provides a path through which cracks generated during processing can propagate, resulting in inferior processability compared to plating having a polygonal Mg ₂ Si phase of 10 µm or more in diameter.

Accordingly, the Mg ₂ Si phase formed in the present invention is improved in corrosion resistance and workability by being present in the Zn phase region formed between the Al phase of the resin phase in the form of a polygonal shape having a diameter of less than 10 µm or needle shape. In general, Al-Zn plated steel sheet has improved corrosion resistance as the Al phase of the dendrite forms the entire skeleton of the plating and is resistant to corrosion, and the Zn phase region formed between the Al phases of the dendrite serves as a sacrificial method. . However, corrosion resistance is still lacking in the cut portion in which the iron is exposed. 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 shape or needle shape having a diameter of less than 10 μm, and the Mg ₂ Si phase of the polygonal shape having a diameter of 10 μm or more and the Chinese character Mg ₂ Si It solves the problem of the phase and improves the corrosion resistance of the Zn phase region to improve the corrosion resistance of the cut portion exposed to the iron. In particular, even if the coating structure is small or the cooling rate is low, the bamboo structure is formed, 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 formed in a Zn phase region in a polygonal shape or a needle shape without a large size of less than 10 μm in diameter, it does not cause cracks during processing or acts as a propagation path of cracks, thereby improving workability. do.

Al-Zn-based alloy plating using the plating composition is started to solidify at 530 ~ 580 ℃ and finishes near 325 ~ 335 ℃. The type, shape and order of phases formed in this process are influenced by Mg content, Si content and Zn content.

In the plating composition range of the present invention, during the solidification process, the Al phase is formed into primary crystals to form a resin phase, and the Si phase starts to form when the solidification temperature is about 500 ° C. In the remaining liquid phase, the Mg ₂ Si phase is first formed, and is formed in a polygonal shape or needle shape of less than 10 μm in diameter. Thereafter, the amorphous MgZn ₂ phase solidifies together with the Zn / Al binary process phase or Zn / Al / MgZn ₂ ternary process phase to form a Zn phase region. The Al phase here is an Al solid solution having Zn in a solid solution containing a small amount of Mg.

In order to form a large number of independent sequins, i.e., sequins with distinct sequin shapes (clearly defined sequins and sequins), 10 or less floral Si phases having a diameter of 100 μm or less per 1 mm ² area of the plating surface must be included. More preferably, it contains less than a dog. When the formula Si (wt%) <Al (wt%) × 0.03 + Mg (wt%) × 0.7 is satisfied, 10 or less floral Si phases having a diameter of 100 μm or less per 1 mm ² area of the plating surface are included. In order to be included, the formula Si (wt%) <Al (wt%) × 0.03 + Mg (wt%) × 0.45 must be satisfied. The above equations are relational expressions for improving the surface properties and workability by minimizing the deposition of the Si phase on the surface and the inside of the plating layer due to extra Si. The above formula is the result of deriving the optimum content of the weight of Si, Al and Mg according to the formation of the sequins through the repeated experiments with different weights of Si, Al and Mg as a formula.

When the Si content becomes more excessive than the amount of Si used for alloy layer thickness control and Mg ₂ Si phase formation, the excess amount forms needle-like acicular Si phase between the plating layers, resulting in inferior processability. In addition, excessive Si is formed on the surface during the solidification of the plating layer, thereby preventing the formation of sequins, which is an outward characteristic of the Al-Zn-based alloy plated steel sheet, thereby deteriorating the plating surface property.

Hereinafter, the reason for limitation of the function and content of the components constituting the plating composition of the present invention will be described.

Zn: 35 ~ 55wt%

Zn dissolves ahead of Fe, the base iron, to retard Fe corrosion. This is called sacrificial corrosion resistance, and sacrificial corrosion resistance is ensured at a content of 35 wt% or more based on the total weight of the composition. If the content of Zn is less than 35wt%, the corrosion resistance of the cut surface is inferior. On the other hand, even if the content of Zn exceeds 55wt% with respect to the total weight of the composition, the sacrificial anticorrosion gradually increases, but the degree is not large, and the Al ₂ O ₃ film formed on the plating surface by the Al component is not formed precisely. The basic corrosion resistance of the alloy plating is reduced. In addition, if the content of Zn exceeds 55wt%, the profit on the cost is not large due to the increase in the specific gravity of the composition.

In order to secure a beautiful surface appearance and corrosion resistance, the ratio of Al (wt%) / Zn (wt%) is preferably 0.9 to 1.8. If the ratio Al (wt%) / Zn (wt%) is less than 0.9 or more than 1.8, the sequins are not clear or the corrosion resistance is inferior.

Mg: 0.3 ~ 2wt%

Mg is an important element for improving corrosion resistance. Mg improves the original corrosion resistance of Al-Zn-based alloy plated steel by covering the surface of the coating layer and the bare iron exposed part with corrosion products including Mg when the coated steel coated with Al-Zn-based alloy plating composition is exposed to the corrosive environment. Let's do it.

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 promote the formation of stable corrosion products in the corrosive environment and serve as a source of the Mg component. As a result, the plating layer surface is quickly covered with a uniform corrosion product. And this corrosion product acts as a stable protective film to improve the corrosion resistance of the plating layer.

In addition, Mg is involved in the sacrificial corrosion resistance of the plated steel together with Zn. Mg is involved in sacrificial anticorrosion in keeping the sacrificial action long.

In addition, Mg reacts with Al to block the diffusion of oxygen, significantly improving the shear corrosion resistance after processing.

In addition, Mg is present as an oxide in the pole surface layer of the plating layer, thereby contributing to the improvement of corrosion resistance, and even when the content is a small amount, the effect of improving corrosion resistance is great.

To form the Mg ₂ Si phase, Mg must be added at least 0.3 wt% based on the total weight of the composition. Preferably, the amount of Mg added is 0.5 wt% or more. In order to form a needle-like or polygonal Mg ₂ Si phase of less than 10 µm in the Zn-phase region of the plating layer, the content should not exceed 2 wt%. When the Mg content is 2wt% or less, the amount of Mg ₂ Si phases is less than 2vol% of the entire plating layer, and the polygons of less than 10 μm in the Zn phase region are not formed in the Chinese character Mg ₂ Si phase formed between Al phases. This is because a phase or acicular Mg ₂ Si phase is formed. In addition, when the amount of Mg added exceeds 2wt%, Mg oxide is easily generated during plating, and defects due to Mg oxide are likely to occur on the plating surface. Preferably, the amount of Mg added is 1 wt% or less. In addition, when the Mg addition amount is less than 1wt%, it is advantageous in terms of cost because air can be used instead of 100% nitrogen in the wiping step of controlling the plating deposition amount.

Si : 0.5 ~ 3wt%

Si is added to suppress the growth of the Fe—Al alloy layer formed at the base iron and the interface, to improve the fluidity of the plating bath to give gloss. If generation of the Fe—Al alloy layer is suppressed, workability is improved.

The addition of Si forms an Mg ₂ Si phase containing Mg. This phase is effective in improving the corrosion resistance of the plated layer front face and the processed portion.

Si should be added 0.5 wt% or more with respect to the total weight of the composition can be expected the effect described above. However, when it is added in excess of 3wt%, needle-shaped Si needles in the plating layer are precipitated to significantly reduce workability, and the excess Si is concentrated and formed on the surface to form sequins, which are outward features of Al-Zn alloy coated steel sheets. It prevents plating surface property from deteriorating.

The Al—Zn based alloy plating composition may be formed of at least one metal selected from Zr or Cr, or at least one metal selected from Sb, Ca, and Sr, or at least one metal selected from Sr, Ca, Be, La, and Ce, or Zr. And at least one metal selected from 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. The weight of the metal is a plating composition, each independently contained in 0.005 ~ 0.2wt%.

Zr and Cr may be added to further improve the corrosion resistance of Al—Zn based alloy plating. Zr further improves the sacrificial corrosion resistance of the Mg intermetallic compound or Zn phase, and Cr increases corrosion resistance of the Al phase.

Sb, Ca and Sr may be added to improve the processability by controlling the shape and size of the Mg ₂ Si phase. Sb, Ca, and Sr can act as nucleation sites of the Mg ₂ Si phase to refine the size or to suppress the formation of the Chinese character Mg ₂ Si phase, thereby improving the workability of Al-Zn alloy plating.

Sr, Ca, Be, La, and Ce may be added to improve the surface and operability of Al-Zn alloy plating. In the Al-Zn alloy plating composition, the molten surface is easily covered with Mg oxide due to the addition of Mg, which causes defects due to adsorption of Mg oxide during plating. Sr, Ca, Be, La and Ce are oxidized before Mg and suppress the oxide generation by Mg while forming a dense oxide film on the surface of the plating bath.

At least one metal selected from Zr, Cr, Sb, Ca, Sr, Ca, Be, La, and Ce should be added at least 0.005 wt% to expect the above-described effect. On the other hand, if it exceeds 0.2wt%, a large amount of dross is generated in the plating bath, thereby causing a problem of damaging the appearance of the plating surface due to the dross adsorption.

And when simultaneously adding at least one metal selected from Zr or Cr, at least one metal selected from Sb, Ca, and Sr and at least one metal selected from Sr, Ca, Be, La, and Ce, the corrosion resistance, workability, and plating surface properties And the operability improvement effect is further increased.

The plating composition of this invention contains the said component, and remainder is Al. Such a plating composition is also allowed to be finely mixed with inevitable impurities of 0.001wt% or less as an element contained according to the situation of raw materials, materials, manufacturing facilities and the like. Particularly in the case of Fe may be incorporated up to 0.5wt% from the manufacturing equipment or steel plated.

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

Method of coating the plating composition on the steel, the step of heating the plating composition having the above-described composition to produce a hot-dip plating bath of 550 ~ 650 ℃, and immersing the steel in the plating bath to coat the plating composition on the surface 5 Cooling to room temperature at a cooling rate of ˜50 ° C./sec.

The steel may be a cold rolled steel sheet or a hot rolled steel sheet or an annealing steel sheet after cold rolling. The steel is then immersed in the plating bath after being adjusted to the plating bath temperature before being immersed in the plating bath. After the steel is immersed in the plating bath, it is pulled up to adjust the coating amount by air wiper using air or nitrogen. If necessary, it can pass through a mini-spingle chamber or galvannealing furnace. At this time, the plating deposition amount is adjusted to 60 ~ 200g / m ² . If the temperature of the plating bath molten metal is less than 550 degreeC, the fluidity of a plating bath will fall and the appearance of a plating film will become poor and plating adhesiveness will fall. On the other hand, if it exceeds 650 ° C, the amount of Fe elution from the internal facilities of the plating bath is increased to increase the dross generation amount, causing insufficient cooling during the solidification process after plating, and causing defects such as flow marks in the plating layer.

If the cooling rate is less than 5 ° C / sec, a large amount of Si phase is formed on the plating surface to prevent the formation of sequins, which is an outward feature of the Al-Zn-based alloy plated steel sheet, thereby deteriorating the plating surface. On the other hand, if the cooling rate exceeds 50 ° C / sec, the surface of the plating layer is roughened by subcooling, there is a problem that 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 structure. When the cooling rate is in the range of 15 to 35 ° C / sec, as the dendrite structure is well developed on the plating surface and the dendrite arm spacing becomes smaller, the number of Al phase layers in the plated cross-sectional structure increases. It has a complicated corrosive path, which further improves corrosion resistance. Therefore, the cooling rate is more preferably in the range of 15 ~ 35 ℃ / sec.

If the plating adhesion amount is less than 60 g / m ^{2, the} corrosion resistance is insufficient. If the plating adhesion amount is more than 200 g / m ² , the plating layer becomes excessively thick due to excessive adhesion amount, thereby deteriorating the adhesion of the plating layer itself and deteriorating the surface gloss and deteriorating the appearance.

Immersion is carried out for 1-3 seconds. If the immersion is less than 1 second, the plating adhesion is lowered. If the immersion is longer than 3 seconds, the alloy layer is thickened in the plating layer, thereby degrading workability.

In this way, the plating composition is coated to form an Al-Zn alloy plating layer on the steel surface, and the Mg ₂ Si phase and the MgZn ₂ phase are included in the plating layer.

The plating layer is a structure in which, in addition to the Mg ₂ Si phase and the MgZn ₂ phase, an Al phase, a Zn phase, an Al / Zn binary process phase and an Al / Zn / MgZn ₂ ternary process phase are mixed.

Specifically, the Mg ₂ Si phase and the MgZn ₂ phase are included in the plating layer, and a large number of uniform and independent sequins are formed on the surface of the plating layer. A large number of independent sequins are uniform in size and the boundaries between sequins and sequins are distinct.

The Mg ₂ Si phase is mainly distributed on the surface of the plating and surrounded by a Zn / Al binary process in the Zn phase region of the plating layer or surrounded by a Zn / Al / MgZn ₂ ternary process to form a polygon or needle having a diameter of less than 10 μm. do.

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

In addition, a plurality of independent sequins are formed by including an average of 10 or less floral Si phases having a diameter of 100 µm or less per 1 mm ² surface of the plating layer, or a floral Si phase having a diameter of 100 µm or less per 1 mm ² surface of the plating layer. It contains less than one on average to form a plurality of independent sequins.

Hereinafter, the present invention will be described in detail in comparison with Examples and other Comparative Examples. However, the following examples are merely to illustrate the invention, the present invention is not limited by the following examples.

Example 1

Manufacture of Plated Steels

Cold rolled steel sheets having a thickness, width, and length of 1.2 mm, 180 mm, and 220 mm, respectively, are immersed in an alkaline solution at 50 ° C. for 30 minutes, and then washed with water to remove foreign substances and oil from the surface to prepare a specimen.

The specimen is annealed and plated. Annealing is carried out in a reducing atmosphere consisting of 10-30% hydrogen and 70-90% nitrogen, and the annealing heat treatment temperature is 750-850 ° C. Here, the annealing is carried out in a reducing atmosphere because Al has a strong affinity with Fe and a high reactivity with oxygen, and thus is easy to form a pointless plating.

For plating, after cooling the annealing test specimen to the plating bath temperature, immerse it in the plating bath for 2 seconds, pull it up, and adjust the plating adhesion amount to 60 ~ 200g / m ² with air wiper using nitrogen. Solidify by cooling to room temperature at the cooling rate of sec. Plating bath temperature shall be 550-650 degreeC.

Table 1 (Unit: wt%)

Table 1 shows the plating bath composition and the component ratio of the invention examples and comparative examples of the present invention.

Example 2

With plating bath  Evaluation of Properties after Plating Specimen

TABLE 2

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

1) Evaluation of Plating Surface

The sequin sharpness and the formation of the plating surface according to the plating composition and the presence or absence of defects were visually observed.

(Double-circle): There is no obvious sequin formation and surface defects

○: distinct sequin formation

(Triangle | delta): A sequin is formed but it is not clear.

X: No sequins formed

In Comparative Examples 3 and 4, sequins were formed, but the boundary between the sequins and the sequins was 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 used the relation Si (wt%) <Al (wt%) × 0.03 + Mg (wt% This is because it did not satisfy) x 0.7, and the difference seems to appear depending on the degree.

On the other hand, Comparative Examples 1 and 2, Comparative Example 5 and Inventive Examples 1 to 3 satisfying the above conditions, all formed a distinctive sequins.

Inventive Examples 4 to 8 including one or more selected from among Sr, Ca, Be, La, and Ce exhibited the most beautiful plating surface properties because defects did not occur with the appearance of sequins with distinct shapes.

2) Evaluation of Machinability

The specimen was bent 180 ° to 1T thickness (bending test) and the cross section was observed under a microscope to determine the crack ratio per unit length. At this time, the crack is limited only to crossing the entire plating layer.

◎: 10% or less crack occurrence rate

○: more than 10% of crack occurrence rate 20% or less

△: more than 20% of crack incidence 30% or less

X: More than 30% of crack incidence

In Comparative Example 2, the crack incidence exceeded 30%. Comparative Example 2 satisfies the conditions Si (wt%) <Al (wt%) × 0.03 + Mg (wt%) × 0.7, but is a subprocess composition in which vol% of Mg ₂ Si phase is formed at 2% or more. Because Mg ₂ Si phase was formed, workability was inferior.

In Comparative Examples 1 and 4, the crack incidence was more than 20% and less than 30%.

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 Comparative Example 4 forms a polygonal or needle-shaped Mg ₂ Si phase of less than 10 μm but does not satisfy the conditions Si (wt%) <Al (wt%) × 0.03 + Mg (wt%) × 0.7. Workability was inferior because needle-shaped Si phase was formed.

Comparative Examples 3 and Inventive Examples 1 to 2 which satisfy the conditions Si (wt%) <Al (wt%) × 0.03 + Mg (wt%) × 0.7 and form a polygonal or needle-shaped Mg ₂ Si phase of less than 10 μm Inventive Examples 6 to 7 and all showed the superior workability compared to Comparative Example 1.

Inventive Examples 3 to 5 and Inventive Example 8 containing at least one selected from Sb, Ca, and Sr have improved processability than before these elements are added, and Comparative Example 5, in which no Mg ₂ Si phase is produced, is Inventive Examples 3 to 5 Compared with, it showed the same level of workability.

3) Evaluation of Plane Corrosion Resistance

According to KS D 9502 (ASTM B-117), rust generation was evaluated by a saline spray test at 5% NaCl at 4000C for 4000 hours.

Shear surfaces of the specimens were covered on all four sides, and after 4000 hours, the surface portion of the specimens were visually observed. At this time, the specimen used a specimen having a plating thickness of 10 ~ 12㎛.

◎: 5% or less red-blue occurrence rate

○: more than 5% red blue incidence rate 10% or less

(Triangle | delta): More than 10% of red-blue incidence rates 30% or less

×: more than 30% of red-blue incidence

In Comparative Example 3, Al (wt%) / Zn (wt%) ratio did not satisfy the conditions of 0.9 to 1.8, showing the most inferior corrosion 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 It showed poor corrosion resistance compared to Example 4 and Inventive Examples 1 and 8.

Inventive Examples 2 to 7 including at least one selected from Zr and Cr have improved corrosion resistance than before these elements are added.

Example 3

Plating bath  Temperature( Plating bath Molten  Temperature) and cooling rate after coating composition coating Plated Evaluation of the Physical Properties of Layers

The composition of the plating composition forming the plating bath was to include Zn: 41.5 wt%, Mg: 1.5 wt%, Si: 2 wt%, and the balance Al and impurities. The steel is then immersed in the plating bath after being adjusted to the plating bath temperature before being immersed in the plating bath.

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

 TABLE 3

1) Evaluation of Plating Surface

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

○: beautiful

△: generation of spots such as surface flow marks

X: Bad stains and poor surface gloss

2) Evaluation of Machinability

The specimen was bent 180 ° to 1T thickness (bending test) and the cross section was observed under a microscope to determine the crack ratio per unit length. At this time, the crack is limited only to crossing the entire plating layer.

◎: 10% or less crack occurrence rate

○: more than 10% of crack occurrence rate 20% or less

△: more than 20% of crack incidence 30% or less

X: More than 30% of crack incidence

2-1) Plating Bath Temperature

When the plating bath temperature was less than 550 ° C., the plating surface appearance was poor and workability was lowered. This seems to be because the plating bath fluidity is lowered. When the plating bath temperature exceeds 650 ℃, stains such as flow marks occurred in the plated layer.

2-2) Cooling Speed

When the cooling rate after the plating is less than 5 ° C / sec, a large amount of Si phase is formed on the surface of the plating to prevent the formation of sequins, thereby reducing the plating surface. And when cooling rate exceeded 50 degreeC / sec, surface gloss fell. In particular, when the cooling rate is 15 ~ 35 ℃ / sec improved corrosion resistance and workability.

As supported by the above experimental results, the Al-Zn-based alloy plating composition including Zn, Mg, Si and the balance Al is plated to form an Mg ₂ Si phase in the plating layer, but the plating layer is controlled by controlling the ratio between components. By controlling the size and shape of the structure and the intermetallic compound, it is confirmed that a plated steel (Al-Zn-based alloy plated steel) excellent in corrosion resistance, workability and plating surface property can be produced.

The present invention is not limited to the above-described embodiments, and various changes can be made without departing from the gist of the present invention, which is understood to be included in the configuration of the present invention.

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

Claims (11)

With respect to the total weight of the plating composition, Zn 35-55wt%, Mg 0.3-2wt%, Si 0.5-3wt% and the balance Al, The plating composition is a plating composition that satisfies the conditions of the following formula (1) and (2). [Equation 1] 0.9 ≤ Al (wt%) / Zn (wt%) ≤ 1.8 [Equation 2] Si (wt%) <Al (wt%) × 0.03 + Mg (wt%) × 0.7 The method of claim 1, The plating composition is a plating composition that satisfies the conditions of the following equation (3). [Equation 3] Si (wt%) <Al (wt%) × 0.03 + Mg (wt%) × 0.45 The method of claim 1, The plating composition further comprises at least one metal selected from Zr, Cr, Sb, Ca, Sr, Be, La and Ce, The weight of the metal is each independently a plating composition containing 0.005 ~ 0.2wt%. An Al-Zn-based alloy plated steel having excellent corrosion resistance, including sequins formed on the surface of the plating layer comprising the plating composition of any one of claims 1 to 3. The method of claim 4, wherein The sequins are Al-Zn-based alloy plating steel excellent in corrosion resistance formed by including an average of 10 or less Si phases having a diameter of 100 μm or less per 1 mm ² area of the plating layer. The method of claim 4, wherein The sequins are Al-Zn-based alloy plated steel having excellent corrosion resistance formed by including an average of one or less Si phase having a diameter of 100 μm or less per 1 mm ² area of the plating layer. The method of claim 4, wherein An Al-Zn-based alloy plated steel having excellent corrosion resistance including a polygonal or needle-like Mg ₂ Si phase and an amorphous MgZn ₂ phase in the Zn phase region in the plating layer. The method of claim 7, wherein The Mg ₂ Si phase is present in the plating surface portion of 10 to 20% or less of the total thickness of the plating, wherein the MgZn ₂ is Al-Zn-based alloy plating steel having excellent corrosion resistance existing throughout the plating layer. The method of claim 4, wherein Al-Zn-based alloy plating steel with excellent corrosion resistance, characterized in that the plating layer comprises a Mg ₂ Si phase of 2vol% or less. The method of claim 4, wherein Excellent corrosion resistance on the surface of the plating layer, including a polygonal or needle-like Mg ₂ Si phase formed in a Zn / Al binary process surrounded by a Zn / Al binary process or surrounded by a Zn / Al / MgZn ₂ ternary process Al-Zn alloy plating steel. Heating the plating composition of any one of claims 1 to 4 to produce a hot-dip plating bath at 550 to 650 ° C; Immersing the steel in the plating bath for 1 to 3 seconds; Plating to a surface of the steel with a plating adhesion amount of 60 to 200 g / m ^{2 by} wiping with nitrogen or air to remove excess plating liquid on the steel to which the plating liquid is attached; And Method for producing a plated steel using a plating composition comprising the step of cooling to 15 to 30 ℃ at a cooling rate of 5 ~ 50 ℃ / sec.

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