KR102110657B1 - Plating composition and method of manufacturing zinc plated steel sheet - Google Patents

Abstract

Plating composition according to an embodiment of the present invention magnesium (Mg): 0.5 ~ 3% by weight, aluminum (Al): 0.5 ~ 10% by weight, silicon (Si): 0.005 ~ 0.1% by weight, titanium (Ti) and boration At least one of titanium (TiB): 0.005 to 0.1% by weight and the balance of zinc (Zn), but the weight ratio of silicon (Si) and the weight ratio of at least one of titanium (Ti) and titanium boride (TiB) 1 : 1 to 1: 5.

Description

Plating composition and method of manufacturing zinc plated steel sheet

The present invention relates to a plating composition and a method of manufacturing a galvanized steel sheet, and more particularly, to a galvanized steel sheet and a manufacturing method thereof.

The existing hot-dip galvanized steel sheet has excellent self-sacrifice, and is widely applied to construction materials and home appliances. When the hot-dip galvanized steel sheet is exposed to a corrosive environment, zinc (Zn) acts as a sacrificial anode for the exposed part of the iron, resulting in the loss of zinc in the plating layer. Such a sacrificial anode action of zinc plays an excellent role in suppressing the generation of rust in the iron in a corrosive environment, but the anode efficiency is somewhat inferior. In order to solve this problem, in recent years, in Japan and Europe, zinc has been added to zinc to produce a dense corrosion product in a corrosive environment, thereby improving anode efficiency to produce high corrosion-resistant plating products that exhibit excellent corrosion resistance. Although zinc may act to increase corrosion resistance as magnesium is added, initial surface activity rapidly increases in a corrosive environment as magnesium is added, resulting in an increase in surface alkalinity. This phenomenon serves to inhibit corrosion resistance during electrodeposition coating after phosphoric acid treatment. When exposed to a corrosive environment after electrodeposition coating, the alkali on the surface of the plating layer also rises, and as a result, the phosphate layer cannot function as a complete barrier. In order to control this phenomenon, it is very important to control the structure of the surface.

A related technology is Korean Patent Publication No. 2016-074753 (published on June 29, 2016, galvanized steel sheet with excellent elongation and manufacturing method thereof).

The problem to be solved by the present invention is to provide a method for manufacturing a galvanized steel sheet having excellent coating corrosion resistance and a plating composition for the same.

Plating composition according to an embodiment of the present invention for achieving the above object is magnesium (Mg): 0.5 ~ 3% by weight, aluminum (Al): 0.5 ~ 10% by weight, silicon (Si): 0.005 ~ 0.1% by weight, At least one of titanium (Ti) and titanium boride (TiB): containing 0.005 to 0.1% by weight and the balance of zinc (Zn), but at least one of the weight ratio of silicon (Si) and titanium (Ti) and titanium boride (TiB) Either weight ratio has a range of 1: 1 to 1: 5.

The composition of aluminum (Al) in the plating composition may be 2 to 5% by weight.

Method for producing a galvanized steel sheet according to another embodiment of the present invention for achieving the above object is magnesium (Mg): 0.5 ~ 3% by weight, aluminum (Al): 0.5 ~ 10% by weight, silicon (Si): 0.005 ~ 0.1 wt%, at least one of titanium (Ti) and titanium boride (TiB): containing 0.005 to 0.1 wt% and the balance of zinc (Zn), but the weight ratio of silicon (Si) and titanium (Ti) and titanium boride ( Preparing a plating bath in which a weight ratio of at least one of TiB) ranges from 1: 1 to 1: 5; Immersing the steel sheet in the plating bath and plating to obtain a galvanized steel sheet; Gas-wiping the galvanized steel sheet; And after the gas wiping, cooling the galvanized steel sheet to room temperature at a cooling rate of 5 to 30 ° C / s. It includes.

The composition of aluminum (Al) in the plating bath of the method for manufacturing the galvanized steel sheet may be 2 to 5% by weight.

In the manufacturing method of the galvanized steel sheet, the temperature of the plating bath may be 400 ~ 520 ℃.

In the method of manufacturing the galvanized steel sheet, the structure of the plating layer formed on the galvanized steel sheet is composed of a ternary process phase consisting of Zn single phase, MgZn ₂ phase, Al and MgZn ₂ phase, and the surface phase fraction of the Zn single phase in the plating layer This can be 20% or more.

The manufacturing method of the galvanized steel sheet, before immersing the steel sheet in the plating bath, annealing the steel sheet at a temperature of 700 ~ 750 ℃ in a reducing atmosphere consisting of 10 ~ 30% hydrogen and 70 ~ 90% nitrogen The heat treatment may further include a step.

According to an embodiment of the present invention, a method of manufacturing a galvanized steel sheet having excellent paint corrosion resistance and a plating composition for the same can be implemented. Of course, the scope of the present invention is not limited by these effects.

1 is a flowchart illustrating a method of manufacturing a galvanized steel sheet according to an embodiment of the present invention.
2 is a photograph of the structure of the plating layer implemented by the method of manufacturing a galvanized steel sheet according to a comparative example of the present invention.
3 is a photograph of the structure of the plating layer implemented by the method of manufacturing a galvanized steel sheet according to an embodiment of the present invention.

Hereinafter, a plating composition according to an embodiment of the present invention and a method of manufacturing a galvanized steel sheet using the same will be described in detail. Terms to be described later are terms appropriately selected in consideration of functions in the present invention, and definitions of these terms should be made based on contents throughout the present specification.

Plating composition

One aspect of the present invention relates to a plating composition that can be applied to a method of manufacturing a galvanized steel sheet. In one embodiment, the plating composition according to one aspect of the present invention, magnesium (Mg): 0.5 ~ 3% by weight, aluminum (Al): 0.5 ~ 10% by weight, silicon (Si): 0.005 ~ 0.1% by weight, titanium At least one of (Ti) and titanium boride (TiB): containing 0.005 to 0.1% by weight and the balance of zinc (Zn), but at least any one of the weight ratio of silicon (Si) and titanium (Ti) and titanium boride (TiB) One weight ratio ranges from 1: 1 to 1: 5.

Magnesium (Mg) added to improve corrosion resistance to zinc (Zn) also improves the alkali on the surface of the plating layer in a corrosive environment, so it is important to control the surface texture of the plating layer produced by the addition of magnesium. The structure of the plating layer plated with a plating bath in which magnesium is added to zinc is composed of a ternary process phase consisting of Zn single phase, MgZn ₂ and Al + MgZn ₂ . Among them, the phases that increase the surface activation of the surface are MgZn ₂ and Al + MgZn ₂ ternary process phases containing Mg. In order to lower the surface alkalinity, the MgZn ₂ phase and the Al + MgZn ₂ ternary process must have a surface phase fraction of 80% or less, and the Zn single phase can be formed by more than 20% to prevent the alkalinity on the surface of the plating layer from rising. In order to control the fraction of these phases, it can be controlled through aluminum (Al) and magnesium (Mg) contents, but it is difficult to express excellent corrosion resistance because aluminum and magnesium contents are possible in a limited input range. On the other hand, aluminum (Al): 0.5wt% ~ 10wt%, magnesium (Mg): 0.5wt% ~ 3wt% with respect to the total weight of the plating composition, which can express corrosion resistance, is added in the range, and the plating surface is excellent corrosion resistance Steel sheet can be obtained.

Magnesium (Mg)

Zinc's sacrificial anode action plays an excellent role in suppressing rust formation of the iron in a corrosive environment, but magnesium is added to solve the problem of poor anode efficiency. Magnesium is added to zinc to produce a dense corrosion product in a corrosive environment, thereby improving anode efficiency, thereby exhibiting excellent corrosion resistance. The content of magnesium directly involved in the formation of the active surface of the plating surface is preferably 0.5% by weight to 3% by weight, and in order to create a process contributing to corrosion resistance, magnesium should be added at least 0.5% by weight, and the magnesium content is 3% by weight If it exceeds, the fractions of the MgZn ₂ and Al + MgZn ₂ ternary processes increase rapidly, making it impossible to control the plating surface activation.

Aluminum (Al)

Aluminum inhibits the formation of magnesium oxide dross in the plating bath and reacts with zinc and magnesium in the plating layer to form a Zn-Al-Mg-based intermetallic compound, which is an element that plays a very important role in improving the phosphate treatment of the plated steel sheet. When the content of aluminum in the plating composition is lower than 0.5% by weight, magnesium cannot be prevented from being oxidized, the ability to inhibit magnesium dross formation is insufficient, and a sufficient amount of Zn-Al-Mg-based intermetallic compound in the surface structure of the plating layer is used. There is a problem that the effect of improving the phosphate treatment property is insufficient because it cannot be secured. When the aluminum content in the plating composition is higher than 10% by weight, the Al single phase on the surface increases, the appearance of the plating surface is poor, and the effect of improving the phosphate treatment is saturated, and the temperature for plating increases, which adversely affects the durability of the plating device. There is a problem, and further, a large amount of Zn-Al-Mg-based intermetallic compounds are formed in the cross-sectional structure of the plated layer, thereby deteriorating spot weldability. Considering this, the content of aluminum in the plating composition may be set to 0.5 to 10% by weight. On the other hand, more preferably, it may be desirable to add 2 to 5% by weight of aluminum based on the total weight of the plating composition. When the aluminum composition satisfies the content range of 2 to 5% by weight, the aluminum resin phase develops without deteriorating the surface appearance, further improving corrosion resistance.

Silicon (Si)

In the limited aluminum and magnesium content range, microelements are added to more effectively express operation and corrosion resistance. The high corrosion-resistant plating bath has a higher aluminum content than the existing zinc plating bath, so iron (Fe) is likely to elute from the steel sheet during plating. To control this, a fine amount of silicon is added. The silicon added for this purpose significantly reduces the amount of Fe dross generated by reducing the amount of Fe eluted from the base iron, and thus it is possible to provide a plated steel sheet having excellent surface appearance. In the plating composition, the content of silicon is preferably 0.005 to 0.1% by weight, for the alloy layer control effect, the silicon addition amount should be 0.005% by weight or more, and when the silicon addition amount exceeds 0.1% by weight, Mg ₂ Si phase is generated. The workability of the plating layer is impaired.

Titanium (Ti) / Titanium Boride (TiB)

Addition of the above-described silicon serves to refine the plating structure, and thus, a large amount of MgZn ₂ phases and ternary process phases are formed on the plating surface to increase surface activation. It is a difficult task to minimize the surface activation while simultaneously reducing the dissolution phenomenon from the steel sheet during plating by adding silicon. In order to solve this problem, by adding at least one selected from Ti and TiB to suppress the refinement of MgZn ₂ phase and ternary process due to silicon addition, it is possible to reduce the increase in alkalinity due to increased surface activation on the plating surface in a corrosive environment. have. At least one or more selected from Ti and TiB forms a metal compound by combining with silicon present in the plating layer upon solidification of the plating layer after plating, thereby reducing the fraction of the activated phase on the plating surface by adding silicon. As a result, the fraction of the Zn single phase on the surface of the plating layer increases and the surface activity decreases. Meanwhile, the TiB and / or Ti addition amount is preferably 0.005 to 0.1% by weight, in order to control the texture of the surface of the plating layer, the TiB and / or Ti addition amount must be 0.005% by weight or more, and the TiB and / or Ti addition amount is 0.1% by weight If it exceeds, titanium and defective metal compounds are excessively generated, and the surface quality of the plating decreases. As can be seen from the above technical content, silicon and titanium interact with each other, so it is possible to obtain the effect of the invention by adding them at an appropriate ratio of two added elements.

When adding silicon and TiB / Ti at the same time, the addition of at least one of titanium (Ti) and titanium boride (TiB) and the addition of silicon (Si) serve to counteract the effects of each other, thereby controlling phase and appearance. The addition ratio should be adjusted in consideration of the improvement. The present inventors have a ratio of the weight ratio of silicon (Si) and the weight ratio of at least one of titanium (Ti) and titanium boride (TiB) in the range of 1: 1 to 1: 5 to provide a suitable corrosion resistance, processability and excellent plating steel. It was confirmed that it can be produced. When the ratio of the weight ratio of silicon (Si) and the weight ratio of at least one of titanium (Ti) and titanium boride (TiB) is less than 1: 1, when the amount of silicon added is large, the surface active phase of the plating surface is increased, and in a corrosive environment. The surface alkalinity of the plating layer cannot be suppressed. When the ratio of the weight ratio of silicon (Si) and the weight ratio of at least one of titanium (Ti) and titanium boride (TiB) is greater than 1: 5, the amount of TiB / Ti added is large, thereby controlling the material Fe dissolution control effect due to silicon addition. It cannot be paid.

When applied to the market of conventional high corrosion-resistant plated steel sheet, it is widely used in the construction materials market due to its excellent corrosion resistance. However, it is very important to secure the corrosion resistance of the electrodeposition coating in the automotive market application. In the present invention, by controlling the microstructure of the surface of the plating layer of the highly corrosion-resistant plated steel sheet, coating is performed by adjusting the added weight ratio of Si and TiB / Ti in the range of 1: 1 to 1: 5 in order to maintain the dryness of the phosphating property of electrodeposition coating. Plated steel with excellent corrosion resistance can be produced.

Hereinafter, a method of manufacturing a galvanized steel sheet using the above-described plating composition will be described.

1 is a flowchart illustrating a method of manufacturing a galvanized steel sheet according to an embodiment of the present invention.

Referring to Figure 1, the method of manufacturing a galvanized steel sheet according to an embodiment of the present invention magnesium (Mg): 0.5 ~ 3% by weight, aluminum (Al): 0.5 ~ 10% by weight, silicon (Si): 0.005 ~ 0.1 At least one of weight percent, titanium (Ti) and titanium boride (TiB): 0.005 to 0.1 weight percent and the balance of zinc (Zn), but the weight ratio of silicon (Si) and titanium (Ti) and titanium boride (TiB) ) At least any one of the weight ratio of 1: 1 to 1: 5, preparing a plating bath as a plating composition (S100); Immersing the steel sheet in the plating bath and plating to obtain a galvanized steel sheet (S300); Gas wiping the galvanized steel sheet (S400); And after the gas wiping, cooling the galvanized steel sheet to room temperature at a cooling rate of 5 to 30 ° C / s (S500); It includes.

In the step (S100) of preparing a plating bath, the description of the plating bath is the same as that of the above-described plating composition, and thus is omitted here.

The temperature of the plating bath may be 400 to 520 ° C. in a step (S300) of immersing the plated steel sheet in the plating bath and performing plating to obtain a galvanized steel sheet. If the temperature of the plating bath is less than 400 ° C, the fluidity of the plating bath is poor, and the appearance of the plating film is poor and the adhesion to the plating is lowered. In addition, the working temperature is preferably a temperature of 40 ° C. or higher than the melting temperature of the plating bath, and when it is less than that, the amount of defects of black spots on the plating surface that inhibit corrosion resistance and surface appearance is increased. When plating is performed at a temperature higher than the melting temperature of the plating bath by 40 ° C or higher, black spots on the plating surface tend to decrease. On the other hand, if the working temperature exceeds 520 ° C, the appearance of the plated steel sheet becomes poor due to excessive oxidation, and the adhesion of the coating film decreases, and after plating, inadequate cooling may cause insufficient cooling to cause defects such as flow marks on the plating layer. .

The structure of the plating layer formed on the galvanized steel sheet is composed of a ternary process phase consisting of Zn single phase, MgZn ₂ phase, Al and MgZn ₂ phase, and the surface phase fraction of the Zn single phase in the plating layer may be 20% or more.

On the other hand, prior to the step (S300) of immersing the plated steel sheet in the plating bath to obtain a galvanized steel sheet by plating, a temperature of 700 to 750 ° C in a reducing atmosphere composed of 10 to 30% hydrogen and 70 to 90% nitrogen is obtained. In the step (S200) of annealing heat treatment of the steel sheet can be performed.

The step of gas wiping the galvanized steel sheet (S400) includes adjusting the plating amount by nitrogen wiping (N2 wiping) or air wiping by immersing the steel sheet in a plating bath and then pulling it up. Can be.

The plating adhesion amount is adjusted to 20 to 300 g / m ² of single-sided plating. This coating weight is 20g / m ² less than if when corrosion resistance is insufficient, and exceeding 300g / m ² becomes over a plating layer thicker by the excess amount of deposition, and at the same time is the adhesion of the plated layer itself decreases, the surface gloss is lowered to deteriorate in appearance or Because.

On the other hand, in the step (S500) of cooling the galvanized steel sheet to room temperature at a cooling rate of 5 to 30 ° C / s, at least a cooling rate of 5 ° C / sec or higher is required to cool the plating layer to a temperature at which the plating layer is completely hardened, and thus the plating layer is irregular. A dense plating layer can be formed without growing in the form of a wave shape. On the other hand, when the cooling rate exceeds 30 ° C / sec, due to the pressure of the cooling air, wrinkles are generated on the surface of the plating layer, and the appearance is deteriorated.

Hereinafter, preferred experimental examples are provided to help understanding of the present invention. However, the following experimental examples are only to help understanding of the present invention, and the present invention is not limited by the following experimental examples.

Experimental Example

In the experimental example of the present invention, a flat coating corrosion resistance evaluation was performed for each zinc alloy plated steel sheet using a plating composition having a composition represented by a weight ratio shown in Table 1. In this experimental example, a cold-rolled steel sheet having a thickness of 0.7 mm was immersed in an alkali solution at 50 ° C. for 30 minutes, and then a specimen was removed by washing with water to remove foreign substances and oil from the surface. This specimen was annealed and then plated. The annealing heat treatment was performed in a reducing atmosphere composed of hydrogen and nitrogen. After plating, the annealing heat-treated specimen is cooled to the plating bath temperature, immersed in the plating bath for 2 seconds, and then pulled up to adjust the plating thickness to about 10 μm by nitrogen wiping, and cooled to room temperature to solidify. A plated steel sheet was prepared under the above conditions, and the electrodeposition coating corrosion resistance of each prepared plated steel sheet was evaluated. Specifically, the incidence of red rust was evaluated by a salt spray test for 1000 hours at NaCl 5%, 35 ° C.

The specimens used in the evaluation were subjected to degreasing treatment for each zinc alloy plated steel sheet prepared before phosphate treatment. At this time, an alkali degreasing agent was used as a degreasing agent, and degreasing treatment was performed in a 3% by weight aqueous solution at 45 ° C for 120 seconds. Thereafter, after rinsing and surface adjustment, it was immersed in a phosphate treatment solution heated to 40 ° C for 120 seconds to form a zinc phosphate-based coating. Thereafter, the specimen obtained by the electrodeposition coating was coated on all four sides of the specimen, and a scratch was formed using a knife in the center. After 1000 hours of corrosion resistance evaluation, the electrodeposition coating on the surface of the specimen was observed with naked eye. Did.

In Table 1, the results of evaluating the coating corrosion resistance were divided into "◎", "○", "△", and "X". "◎" item means that the peeling of the scratched part is less than 3mm, "○" item means that the peeling of the scratched part is less than 7mm, and "△" means that the peeling of the scratched part is less than 10mm, "X "The item means that the peeling of the scratched portion is 10 mm or more.

division Zn Al Mg Si TiB Si: TiB
Addition ratio stamp
Corrosion resistance Plating surface Zn single phase (area%) Comparative Example 1 Bal. 0.2 0 0 0 - X 100 Comparative Example 2 Bal. One One 0.01 0.005 1: 0.5 △ 18 Comparative Example 3 Bal. 2 1.5 0.01 0.005 1: 0.5 △ 15 Comparative Example 4 Bal. 5 3 0.01 0.005 1: 0.5 △ 10 Example 1 Bal. One One 0.01 0.01 1: 1 ○ 26 Example 2 Bal. 2 1.5 0.01 0.02 1: 2 ◎ 32 Example 3 Bal. 2 1.5 0.005 0.02 1: 4 ◎ 38 Example 4 Bal. 5 3 0.02 0.05 1: 2.5 ◎ 21

Referring to Comparative Example 1, when applying a plating composition containing aluminum (Al): 0.2% by weight and the remainder of zinc (Zn), in the coating corrosion resistance evaluation, the scratch coating peeling is 10 mm or more, and the Zn single phase The area ratio was found to be 100%.

Referring to Comparative Example 2, magnesium (Mg): 1% by weight, aluminum (Al): 1% by weight, silicon (Si): 0.01% by weight, titanium boride (TiB): 0.005% by weight and the balance of zinc (Zn) Including, but when applying a plating composition having a weight ratio of silicon (Si) and a weight ratio of titanium boride (TiB) of 1: 0.5, in the coating corrosion resistance evaluation, scratch coating peeling is less than 10 mm, the area ratio of Zn single phase on the surface of the plating layer Was found to be 18%.

Referring to Comparative Example 3, magnesium (Mg): 1.5% by weight, aluminum (Al): 2% by weight, silicon (Si): 0.01% by weight, titanium boride (TiB): 0.005% by weight and the balance of zinc (Zn) Including, but when applying a plating composition having a weight ratio of silicon (Si) and a weight ratio of titanium boride (TiB) of 1: 0.5, in the coating corrosion resistance evaluation, scratch coating peeling is less than 10 mm, the area ratio of Zn single phase on the surface of the plating layer Was found to be 15%.

Referring to Comparative Example 4, magnesium (Mg): 3% by weight, aluminum (Al): 5% by weight, silicon (Si): 0.01% by weight, titanium boride (TiB): 0.005% by weight and the balance of zinc (Zn) Including, but when applying a plating composition having a weight ratio of silicon (Si) and a weight ratio of titanium boride (TiB) of 1: 0.5, in the coating corrosion resistance evaluation, scratch coating peeling is less than 10 mm, the area ratio of Zn single phase on the surface of the plating layer Was found to be 10%.

Referring to Comparative Example 4, magnesium (Mg): 3% by weight, aluminum (Al): 5% by weight, silicon (Si): 0.01% by weight, titanium boride (TiB): 0.005% by weight and the balance of zinc (Zn) Including, but when applying a plating composition having a weight ratio of silicon (Si) and a weight ratio of titanium boride (TiB) of 1: 0.5, in the coating corrosion resistance evaluation, scratch coating peeling is less than 10 mm, the area ratio of Zn single phase on the surface of the plating layer Was found to be 10%.

Referring to Example 1, magnesium (Mg): 1% by weight, aluminum (Al): 1% by weight, silicon (Si): 0.01% by weight, titanium boride (TiB): 0.01% by weight, and the balance of zinc (Zn) Including, but when applying a plating composition having a weight ratio of silicon (Si) and a weight ratio of titanium boride (TiB) of 1: 1, the coating peeling of the scratch in the coating corrosion resistance evaluation is less than 7 mm, and the area ratio of Zn single phase on the surface of the plating layer Was found to be 26%.

Referring to Example 2, magnesium (Mg): 1.5% by weight, aluminum (Al): 2% by weight, silicon (Si): 0.01% by weight, titanium boride (TiB): 0.02% by weight and the balance of zinc (Zn) Including, but when applying a plating composition having a weight ratio of silicon (Si) and a weight ratio of titanium boride (TiB) of 1: 2, in the coating corrosion resistance evaluation, the scratch coating peeling is less than 7 mm, the area ratio of Zn single phase on the surface of the plating layer Was found to be 32%.

Referring to Example 3, magnesium (Mg): 1.5% by weight, aluminum (Al): 2% by weight, silicon (Si): 0.005% by weight, titanium boride (TiB): 0.02% by weight and the balance of zinc (Zn) Including, but when applying a plating composition having a weight ratio of silicon (Si) and a weight ratio of titanium boride (TiB) of 1: 4, in the coating corrosion resistance evaluation, abrasion coating peeling is less than 7 mm, the area ratio of Zn single phase on the surface of the plating layer Was found to be 38%.

Referring to Example 4, magnesium (Mg): 3% by weight, aluminum (Al): 5% by weight, silicon (Si): 0.02% by weight, titanium boride (TiB): 0.05% by weight and the balance of zinc (Zn) Including, but when applying a plating composition having a weight ratio of silicon (Si) and a weight ratio of titanium boride (TiB) of 1: 2.5, in the coating corrosion resistance evaluation, the scratch coating peeling is less than 7 mm, and the area ratio of the Zn single phase on the surface of the plating layer Was found to be 21%.

Referring to Comparative Example 1, when applying a plating composition that does not contain magnesium, silicon, and titanium boride, it can be seen that the coating corrosion resistance is very poor because the peeling of the coating is more than 10 mm in the evaluation of coating corrosion resistance.

Referring to Comparative Examples 2 to 4, magnesium (Mg): 0.5 to 3% by weight, aluminum (Al): 0.5 to 10% by weight, silicon (Si): 0.005 to 0.1% by weight, titanium boride (TiB): Even if a plating composition containing 0.005 to 0.1% by weight and the balance of zinc (Zn) is applied, the weight ratio of silicon (Si) and at least one of titanium (Ti) and titanium boride (TiB) are 1: 1 to 1 When the range of: 5 is not satisfied, it can be seen that the surface phase fraction of the Zn single phase in the plating layer is less than 20%, so that the alkalinity of the surface of the plating layer is increased and thus the corrosion resistance during electrodeposition coating after phosphoric acid treatment is not excellent.

On the other hand, referring to Examples 1 to 4, magnesium (Mg): 0.5 to 3 wt%, aluminum (Al): 0.5 to 10 wt%, silicon (Si): 0.005 to 0.1 wt%, titanium (Ti ) And at least one of titanium boride (TiB): 0.005 to 0.1% by weight and the balance of zinc (Zn), but the weight ratio of silicon (Si) and at least one of titanium (Ti) and titanium boride (TiB) When the weight ratio has a range of 1: 1 to 1: 5, when a plating composition is applied, it can be confirmed that the surface phase fraction of the Zn single phase in the plating layer is 20% or more and the coating corrosion resistance is relatively excellent.

2 is a photograph of the structure of the plating layer implemented by the method of manufacturing a galvanized steel sheet according to the comparative example of the present invention, and FIG. 3 is a photograph of the structure of the plating layer implemented by the method of manufacturing a galvanized steel sheet according to the embodiment of the present invention.

The plating layer shown in Figure 2 is magnesium (Mg): 1% by weight, aluminum (Al): 2.5% by weight, silicon (Si): 0.01% by weight, titanium boride (TiB): 0.005% by weight and the balance of zinc (Zn) Including, but implemented by applying a plating composition having a weight ratio of silicon (Si) and a weight ratio of titanium boride (TiB) of 1: 0.5, it can be confirmed that the surface phase fraction of the Zn single phase in the plating layer is less than 20%.

The plating layer shown in Figure 3 is magnesium (Mg): 1% by weight, aluminum (Al): 2.5% by weight, silicon (Si): 0.01% by weight, titanium boride (TiB): 0.02% by weight and the balance of zinc (Zn) Including, but by implementing a plating composition having a weight ratio of silicon (Si) and a weight ratio of titanium boride (TiB) of 1: 2, it can be confirmed that the surface phase fraction of the Zn single phase in the plating layer is 20% or more.

In the above, although the description has been mainly focused on the embodiment of the present invention, various changes or modifications can be made at the level of those skilled in the art. It can be said that such modifications and variations belong to the present invention without departing from the scope of the present invention. Therefore, the scope of the present invention should be judged by the claims set forth below.

Claims (7)

Magnesium (Mg): 0.5 to 3% by weight, aluminum (Al): 0.5 to 10% by weight, silicon (Si): 0.005 to 0.02% by weight, titanium boride (TiB): 0.01 to 0.05% by weight and the balance of zinc (Zn ),
Characterized in that the weight ratio of silicon (Si) and the weight ratio of titanium boride (TiB) is added in a range of 1: 1 to 1: 4 to suppress the refinement of MgZn ₂ phase and ternary process,
Plating composition. According to claim 1,
Characterized in that the composition of aluminum (Al) is 2 to 5% by weight,
Plating composition. Magnesium (Mg): 0.5 to 3% by weight, aluminum (Al): 0.5 to 10% by weight, silicon (Si) 0.005 to 0.02% by weight, titanium boride (TiB): 0.01 to 0.05% by weight and the balance of zinc (Zn) Including,
Preparing a plating bath in which the weight ratio of silicon (Si) and titanium boride (TiB) is added in a range of 1: 1 to 1: 4 to suppress the refinement of MgZn ₂ phase and ternary process;
Immersing the steel sheet in the plating bath and plating to obtain a galvanized steel sheet;
Gas-wiping the galvanized steel sheet; And
After the gas wiping, cooling the galvanized steel sheet to room temperature at a cooling rate of 5 to 30 ° C / s; Including,
The structure of the plating layer formed on the galvanized steel sheet is composed of a ternary process phase consisting of Zn single phase, MgZn ₂ phase, Al and MgZn ₂ phase, wherein the surface phase fraction of the Zn single phase in the plating layer is 21% to 38%. Made with,
Method for manufacturing galvanized steel sheet. The method of claim 3,
The composition of aluminum (Al) in the plating bath is characterized in that 2 to 5% by weight,
Method for manufacturing galvanized steel sheet. The method of claim 3,
The temperature of the plating bath is characterized in that 400 ~ 520 ℃,
Method for manufacturing galvanized steel sheet. delete The method of claim 3,
Before immersing the steel sheet in the plating bath, further comprising the step of annealing the steel sheet at a temperature of 700 ~ 750 ℃ in a reducing atmosphere consisting of 10 ~ 30% hydrogen and 70 ~ 90% nitrogen,
Method for manufacturing galvanized steel sheet.

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