KR102045656B1 - Zn-Al-Mg alloy plated steel sheet having excellent corrosion resistance and manufacturing method for the same - Google Patents

Abstract

Zinc-aluminum-magnesium alloy plated steel sheet according to an embodiment of the present invention, the base steel sheet and a molten zinc-aluminum-magnesium plating layer, the plating layer, in weight%, Al: 0.5 to 3%, Mg: 0.5 ~ 2.5%. The surface of the base steel sheet including the remaining Zn and other unavoidable impurities and forming an interface with the plating layer may be formed with a curved fine roughness crossing the cold rolling groove formed along the longitudinal direction of the base steel sheet.

Description

Zn-Al-Mg alloy plated steel sheet having excellent corrosion resistance and manufacturing method for the same}

The present invention relates to a zinc-aluminum-magnesium alloy plated steel sheet used in automobile panels, home appliances, and buildings, and to a method of manufacturing the same. It is about.

Hot-dip galvanized steel sheet has a simple manufacturing process compared to electro-galvanized steel sheet, the product price is low, and the demand is expanding to building materials, home appliances and automobiles. Recently, as the price of zinc increases, the demand for hot-dip zinc-aluminum or hot-dip zinc-aluminum-magnesium alloy plated steel sheets, which can secure excellent corrosion resistance even with a smaller coating amount, has been developed.

Representative zinc-aluminum alloy plated steel sheets include zinc-55% aluminum plated steel sheets. Since zinc-55% aluminum plated steel sheet has higher aluminum content than zinc content, sacrificial corrosion protection is lowered and corrosion is prematurely exposed at the site where an underlying metal such as a cut surface is exposed. There is a problem that occurs. In addition, in the case of hot-dip galvanized-55% aluminum plating, the plating bath temperature should be set as high as 600 ° C., so dross is generated in the plating bath severely, and plating workability is degraded due to equipment erosion in the plating bath such as sink rolls. There is a problem that the life is shortened.

Patent Document 1 proposes a zinc-aluminum-magnesium alloy plated steel sheet having a total content of aluminum and magnesium of 5 to 15 wt%. Since the total content of aluminum and magnesium is 5 to 15%, it shows excellent corrosion resistance and shows suitable quality properties for building materials. However, due to the high alloying components of aluminum and magnesium in the plating layer, it is disadvantageous in terms of weldability and workability. Application is limited.

In addition, the solidification initiation temperature of the zinc-aluminum-magnesium alloy plating layer having a total content of aluminum and magnesium of 10wt% or less varies slightly depending on the content of aluminum and magnesium, but is in the range of 400 to 420 ° C., and the zinc-aluminum-magnesium ternary process The final solidification end temperature of the tissue is around 340 ° C, which may cause flow pattern defects due to the selective oxidation of magnesium in the liquid-solid phase temperature range. This is because aluminum and magnesium are concentrated in the unsolidified molten metal pool during the solidification of the plating layer, and the higher the concentration of magnesium is, the easier the oxidation is, resulting in nonuniformity of fluidity.

Focusing on this point, the researchers have proposed a hot-dip galvanized-aluminum-magnesium alloy plated steel sheet which can achieve excellent corrosion resistance while reducing the aluminum and magnesium content in the plating layer as much as possible.

Japanese Patent Laid-Open No. 10-226865 (published Aug. 25, 1998)

According to one aspect of the present invention, a zinc-aluminum-magnesium alloy plated steel sheet which effectively secures corrosion resistance and a manufacturing method thereof may be provided.

The subject of this invention is not limited to what was mentioned above. Those skilled in the art will have no difficulty understanding the additional subject matter of the present invention from the general contents of this specification.

Zinc-aluminum-magnesium alloy plated steel sheet excellent in corrosion resistance according to an embodiment of the present invention, the base steel sheet and a molten zinc-aluminum-magnesium plating layer, the plating layer, in weight%, Al: 0.5 to 3%, Mg: 0.5-2.5%. The surface of the base steel sheet including the remaining Zn and other unavoidable impurities and forming an interface with the plating layer may be formed with a curved fine roughness crossing the cold rolling groove formed along the longitudinal direction of the base steel sheet.

The fine depth of the irregularities is 0.1 ~ 2㎛, the average width is 0.1 ~ 0.5㎛, the average interval may be 50 ~ 300㎛.

In the method for producing a zinc-aluminum-magnesium alloy plated steel sheet excellent in corrosion resistance according to an embodiment of the present invention, a curved fine iron is applied to the surface of the steel sheet by a rotary brush, and in weight%, Al: 0.5 to 3%, Mg: 0.5-2.5%. A plated layer may be formed by immersing the base steel sheet in a molten zinc-aluminum-magnesium plating bath containing the remaining Zn and other unavoidable impurities.

The curved fine roughness may be formed to cross a straight cold rolling groove formed along the longitudinal direction on the surface of the steel sheet by cold rolling.

The average depth of the curved fine irregularities is 0.1 ~ 2㎛, the average width is 0.1 ~ 0.5㎛, the average spacing of the fine irregularities may be 50 ~ 300㎛.

Zinc-aluminum-magnesium excellent in corrosion resistance according to an embodiment of the present invention? An alloy plated steel sheet and a method for manufacturing the same can provide a plated steel sheet and a method of manufacturing the same having improved corrosion resistance by effectively controlling the Mg concentration at the surface side of the plated layer.

The present invention relates to a zinc-aluminum-magnesium alloy plated steel sheet excellent in corrosion resistance and a method for manufacturing the same, hereinafter, preferred embodiments of the present invention will be described. Embodiments of the invention may be modified in various forms, the scope of the invention should not be construed as limited to the embodiments described below. These embodiments are provided to explain in detail the present invention to those skilled in the art.

Method for producing a zinc-aluminum-magnesium alloy plated steel sheet excellent in corrosion resistance according to an embodiment of the present invention, the base steel sheet and the molten zinc-aluminum-magnesium plating layer, the plating layer, in weight%, Al: 0.5 ~ 3%, Mg: 0.5-2.5%. Remaining Zn and other unavoidable impurities.

The steel sheet of the present invention may include all steel sheets provided in hot dip galvanizing, but the steel sheet according to the embodiment of the present invention may be a cold rolled steel sheet.

Hereinafter, the reason for component limitation of the plating layer of this invention is demonstrated in detail. Hereinafter, unless otherwise indicated,% of the present invention is based on weight.

In general, galvanized steel sheets containing zinc components include zincite (ZnO), hydrozingite (Zn ₅ (CO ₃ ) ₂ (OH) ₆ ), and Simonkolleite (Zn ₅₎ (OH). ) ₈ Cl ₂ ) and the like, and among these, Simoncolite is known to have excellent corrosion inhibitory effect as a dense corrosion product. When a large amount of MgZn ₂ phase is formed on the surface side of the plating layer, it is possible to form mainly Simon collite under a corrosive environment, and exhibit excellent corrosion resistance. That is, when the Mg component is concentrated on the surface side of the plated layer, it means that a large amount of MgZn ₂ phase is formed on the surface side of the plated layer, thereby further improving the corrosion resistance of the plated steel sheet in a corrosive environment.

Therefore, the zinc-aluminum-magnesium alloy plated steel sheet of the present invention intends to form more MgZn ₂ phase on the surface of the plated layer, thereby further improving the corrosion resistance of the plated steel sheet.

Mg is an element added for improving corrosion resistance. Therefore, the plating layer of the present invention may include 0.5% or more of Mg for improving corrosion resistance. On the other hand, when the Mg content is excessively added in the plating layer, while the effect of improving the corrosion resistance due to the addition of Mg is saturated, the workability and weldability of the plated steel sheet may be inferior. Therefore, the present invention can limit the upper limit of the Mn content contained in the plating layer to 2.5%.

In particular, when the Mn content contained in the coating layer not more than 2.5%, while the plating layer solidification when Zn single phase that first the solidification after the Zn-Al-MgZn ₂ 3 won process organization and MgZn ₂ 2 won step tissue formation, contained in the plated layer When the Mg content exceeds 2.5%, the MgZn ₂ phase, not the Zn single phase, is crystallized as a primary tablet, so that the concentration of Mg that is concentrated at the surface of the plating layer may be lowered compared to the increase of the Mg content. That is, when the Mn content contained in the plating layer exceeds 2.5%, the increase in the amount of Simon collite formation may decrease in the corrosive environment despite the increase in the amount of Mg added. Therefore, the effect of improving the corrosion resistance due to the addition of Mg is saturated. Can be.

Al is an element contributing to securing adhesion between the plated layer and the base steel sheet. In order to achieve such an effect, the present invention may limit the content of Al contained in the plated layer to 0.5% or more. On the other hand, when the Al content is excessively added in the plating bath, it is inevitable to increase the temperature of the plating bath, which may cause operational difficulties due to the increase in upper dross and the decrease in wettability. Therefore, the upper limit of the Al content included in the plating layer of the present invention may be limited to 2.5%.

The zinc-aluminum-magnesium alloy plated steel sheet having excellent corrosion resistance according to an embodiment of the present invention includes a base steel sheet and a hot dip zinc-aluminum-magnesium plating layer, and the surface of the base steel sheet forming an interface with the plating layer is Curved fine roughness crossing the cold rolling groove formed along the longitudinal direction of the base steel sheet may be formed.

In general, the surface of the base steel sheet provided by cold rolling may be provided with a cold rolling groove formed along a direction parallel to the longitudinal direction of the base steel sheet. Cold rolled groove is a kind of scratch that occurs naturally by contact with cold rolled roll during cold rolling. It occurs parallel to the direction of steel sheet. Experiment shows that cold rolled groove has little effect on solidification nucleation of Zn single phase. It became.

The fine roughness of the present invention may be formed by a polishing operation, and preferably by a rotary polishing brush. Therefore, the fine roughness of the present invention is not formed in a specific direction, and in particular, the fine roughness formed by the rotary polishing brush may be formed to face in all directions. Therefore, the micro roughness of the present invention may be formed to extend to cross the cold rolling grooves formed on the surface of the steel sheet. In addition, the bar may be formed by the rotary polishing brush of the present invention, and may be formed in a curved shape as compared with the cold rolled groove.

The researchers of the present invention carried out a study on improving the corrosion resistance of the plated layer containing Al and Mg of the above-mentioned content, it was found that there is a constant relationship between the reaction surface area of the steel sheet and the corrosion resistance of the plated steel sheet . That is, Al: 0.5 to 3%, Mg: 0.5 to 2.5%. When forming a plated layer containing the remaining Zn and other unavoidable impurities, it was confirmed that the desired corrosion resistance improvement effect occurs only when the size of the fine roughness formed on the steel sheet satisfies a predetermined requirement. That is, it was confirmed that the corrosion resistance of the plating layer can be improved by providing roughness of the surface of the steel sheet without excessively adding Mg content in the plating layer.

In the base steel sheet of the same size, the rougher the surface on which the base steel plate and the plating solution reacts may promote the formation of a Zn single phase at the interface side of the plating layer. That is, solidification nucleation is promoted as the actual area of the base steel sheet increases as the actual area increases, and the formation of the Zn single phase can be promoted at the interface side of the plated layer. As the solidification of the Zn single phase proceeds, the Mg component becomes a plating solution. Will diffuse and move. Accordingly, the concentration of the plating layer surface side of the Mg component relatively increases as compared to the interface side of the coating layer, which may mean that the MgZn ₂ 2 won process on the surface of the plating layer structure formed much.

In the case of fine roughness formed by the polishing, the width of the fine roughness is widened with the progress of the polishing, while the depth of the fine roughness is reduced. In addition, as the polishing operation proceeds, the spacing between fine roughness becomes narrow. Therefore, the effect of increasing the concentration of the Mg component on the surface of the plating layer can be obtained only when fine roughness having an appropriate level of size is formed on the surface of the steel sheet.

That is, the average depth and width of the fine irregularities of the present invention may be 0.1-2 μm and 0.1-0.5 μm, respectively, and the average interval of fine irregularities may be 50-300 μm. If the size of the fine roughness is out of the range, it is because it is impossible to secure the projected area of the base steel sheet to the extent that can promote the formation of Zn single phase at the plating layer interface side. However, in the present specification, the depth of fine irregularities may be interpreted to mean the height of fine irregularities. In addition, when the average width of micro-corrugations exceeds 300 µm, the size of the sequins formed in the plating layer tends to exceed 300 µm, which is not preferable in terms of surface appearance.

Hereinafter, the manufacturing method of the present invention will be described in more detail.

In the method for producing zinc-aluminum-magnesium alloy plated steel sheet excellent in corrosion resistance according to an embodiment of the present invention, a curved fine iron is applied to the surface of the steel sheet by a rotary brush, and the molten zinc-aluminum-magnesium plating bath is applied. The plated layer may be formed by dipping the base steel sheet.

The abrasive member provided in the formation of the fine roughness of the present invention may be sandpaper of 150 to 250 mesh in consideration of the size and roughness providing efficiency of the unevenness formed on the surface of the steel sheet, preferably of 200 to 230 mesh sandpaper. Can be. In addition, the polishing member may be provided to the rotary brush to perform the surface polishing operation of the steel sheet, preferably the curved fine roughness formed by the polishing operation to cross the straight cold rolling groove formed on the surface of the steel sheet Polishing can be performed.

The average depth and width of the fine irregularities formed by the rotatable brush may be 0.1 to 2 μm and 0.1 to 0.5 μm, respectively, and the average interval of the fine irregularities may be 50 to 300 μm. The size and spacing of the fine roughness of the present invention correspond to the fine roughness size and spacing of the above-described plated steel sheet, and the description thereof will be replaced by the description of the fine roughness and spacing of the above-described plated steel sheet.

In addition, the plating bath of this invention is Al: 0.5-3%, Mg: 0.5-2.5% by weight%. Remaining Zn and other unavoidable impurities. The composition content of the plating bath of the present invention corresponds to the composition content of the above-described plating layer, and the description of the reason for limiting the composition content of the plating bath of the present invention is replaced by the description of the reason for limiting the composition content of the plating layer described above. do.

Hereinafter, the present invention will be described in more detail with reference to Examples.

(Example)

After degreasing the surface of the specimen with a 0.8 mm thick cold carbon steel sheet, the specimens were polished under the conditions shown in Table 1 below to give roughness to the specimen surface, and the size of the fine roughness flattened on each specimen surface was measured. In Table 1, the number of times of polishing refers to the number of times the polishing was performed with sandpaper of # 220 mesh. After imparting roughness, plating was performed by immersion in a plating bath provided with the composition contents of Table 1, and gas plating was performed by nitrogen gas to prepare a plated steel sheet. A salt spray test (a salt spray standard test according to KS-C-0223) was carried out on each plated steel sheet, and it was passed until the reddish blue area on the surface of each specimen reached 5% of the total plated steel sheet area. The time was measured.

division grinding
collection Fine iron average size (㎛) Plating layer composition
(wt%) 5% blue red
Brine spraying time (Hr) Remarks width depth interval Al Mg 1-1 One 0.08 0.5 500 0.5 0.5 240 Comparative Example 1 1-2 5 0.1 0.3 250 0.5 0.5 360 Inventive Example 1 1-3 20 0.2 0.2 50 0.5 0.5 360 Inventive Example 2 1-4 50 0.3 0.05 40 0.5 0.5 260 Comparative Example 2 2-1 One 0.08 0.5 480 2 2 480 Comparative Example 3 2-2 5 0.1 0.3 250 2 2 560 Inventive Example 3 2-3 20 0.2 0.2 50 2 2 560 Inventive Example 4 2-4 50 0.3 0.06 40 2 2 480 Comparative Example 4 3-1 2 0.09 0.5 400 2.5 3 960 Comparative Example 5 3-2 5 0.1 0.3 250 2.5 3 960 Comparative Example 6 3-3 20 0.2 0.2 50 2.5 3 960 Comparative Example 7 3-4 50 0.4 0.05 40 2.5 3 960 Comparative Example 8

Inventive Examples 1 and 2, compared with Comparative Example 1 in which the surface of the specimen was polished once, increased the time until the occurrence of 5% red blue, about 120 hours, and thus it was confirmed that the corrosion resistance of the plated steel sheet was effectively improved. That is, even when the plating layer was formed by being immersed in the plating bath under the same conditions, it can be confirmed that the corrosion resistance of Inventive Examples 1 and 2 was significantly improved compared to Comparative Example 1. On the other hand, in the case of Comparative Example 2, the surface of the specimen was excessively polished before plating, and the time until the occurrence of 5% red blue color was improved by about 20 hours compared to Comparative Example 1, and thus the effect of improving the corrosion resistance compared to Inventive Examples 1 and 2 It can be seen that is not large.

Inventive Examples 3 and 4, compared to Comparative Example 3, which performed the polishing of the surface of the specimen once, increased the time until the occurrence of 5% red blue, about 80 hours, and thus it was confirmed that the corrosion resistance of the plated steel sheet was effectively improved. That is, Comparative Example 3, Inventive Examples 3 and 4 are all immersed in the plating bath under the same conditions, even though the plating layer was formed, it can be seen that the corrosion resistance of Inventive Examples 3 and 4 significantly improved compared to Comparative Example 3. On the other hand, in the case of Comparative Example 4, the surface of the specimen was excessively polished before plating, and thus it was confirmed that the time until the occurrence of 5% red blue compared to Comparative Example 1 was the same level.

In the case of Comparative Examples 5 to 8, the Mg content in the plating layer exceeds the range of the present invention, and it is confirmed that the corrosion resistance is not improved despite the polishing of the specimen surface before plating.

Therefore, the zinc-aluminum-magnesium alloy plated steel sheet excellent in corrosion resistance according to an embodiment of the present invention and a method of manufacturing the same can effectively cause the concentration of Mg concentration on the surface of the plated layer to effectively improve the corrosion resistance of the plated steel sheet.

Although the present invention has been described in detail through the embodiments, other forms of embodiments are also possible. Therefore, the spirit and scope of the claims set forth below are not limited to the embodiments.

Claims (5)

A steel sheet and a molten zinc-aluminum-magnesium plating layer,
The plating layer, in weight%, Al: 0.5 to 3%, Mg: 0.5 to 2.5%. Containing the remaining Zn and other unavoidable impurities,
On the surface of the base steel sheet forming an interface with the plating layer is formed a curved fine roughness crossing the cold rolling groove formed along the longitudinal direction of the base steel sheet,
The average depth of the fine roughness is 0.1 ~ 2㎛, the average width is 0.1 ~ 0.5㎛, the average spacing of the fine roughness is 50 ~ 300㎛, zinc-aluminum-magnesium alloy plated steel sheet excellent in corrosion resistance. delete A curved brush is applied to the surface of the steel sheet by a rotating brush,
By weight%, Al: 0.5-3%, Mg: 0.5-2.5%. Forming a plating layer by immersing the base steel sheet in a molten zinc-aluminum-magnesium plating bath containing the remaining Zn and other unavoidable impurities,
The average depth of the fine roughness is 0.1 ~ 2㎛, the average width is 0.1 ~ 0.5㎛, the average spacing of the fine roughness is 50 ~ 300㎛, the manufacturing method of zinc-aluminum-magnesium alloy plated steel sheet excellent in corrosion resistance. The method of claim 3,
The curved fine roughness is formed to cross a straight cold rolling groove formed in the longitudinal direction on the surface of the base steel sheet by cold rolling, excellent corrosion resistance zinc-aluminum-magnesium alloy plated steel sheet manufacturing method. delete