KR20150066339A - Manufacturing Method of High Strength Zn-Al-Mg Hot-dip Galvanized Steel Sheet Having Excellent Zn Adhesion Property and Steel Sheet by the Same Method - Google Patents

Abstract

The present invention relates to a high strength Zn-Al-Mg hot-dip galvanized steel sheet having excellent Zn adhesion property and manufacturing method thereof, by which there is no non-plated area by removing Si, Mn-based oxide formed on a surface after an annealing heat treatment. Provided is a method of manufacturing a Zn-Al-Mg hot-dip galvanized steel sheet comprising: an annealing heat treatment step of a cooling treatment after firstly heat-treating, at 700°C~900°C, a cold steel sheet consisting of C 0.05 to 0.3weight%, Si 0.5 to 2.0 weight% and Mn 0.5 to 3.0 weight%; a shot blasting step to remove oxide on a surface of the steel sheet by spraying shot balls on the heat-treated cold steel sheet; and a hot-dip step of performing plating by secondly heat-treating, at 420 to 550°C, the cold steel sheet from which the oxide is removed and immersing the cold steel sheet in a Zn-Al-Mg hot-dip galvanized bath. Provided is the Zn-Al-Mg hot-dip galvanized steel sheet comprising: the steel sheet consisting of C 0.05 to 0.3weight%, Si 0.5 to 2.0 weight% and Mn 0.5 to 3.0 weight%; and a Zn-Al-Mg hot-dip galvanized layer on a surface of the steel sheet, wherein the Zn-Al-Mg hot-dip galvanized steel sheet having an average surface profile of 0.5-3.0μm is supplied to the surface of the steel sheet.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-dip Zn-Al-Mg alloy hot-dip galvanized steel sheet excellent in plating adhesion,

The present invention relates to a high-strength zinc-aluminum-magnesium alloy cold-rolled hot-dip galvanized steel sheet excellent in plating adhesion and a method for manufacturing the same.

Zinc-aluminum-magnesium alloy coated steel sheet having a plating layer showing inherent excellent corrosion-preventing properties which can be obtained from zinc-based plating while having a small amount of zinc adhered to the world is attracting much attention due to the decrease in zinc reserves. Further, the use of such a zinc-aluminum-magnesium alloy coated steel sheet as an automobile is considered, and studies are underway.

On the other hand, efforts to reduce the weight of the automobile body through the enhancement of the strength of the steel plate have been made as one of solutions to the fuel efficiency regulation of the automobile. As one of the manufacturing methods of such high strength steel, there is a method of ensuring high strength and high ductility by Transformation Induced Plasticity (hereinafter simply referred to as 'TRIP'). As such a TRIP steel, 0.05 to 0.3% by weight of C, 0.5 to 2.0% by weight of Si and 0.5 to 3.0% by weight of Mn are added as a basic alloying element in steel and subjected to cold rolling, , Bainite transformation is performed at a temperature of about 400 캜, and residual austenite finely homogeneously dispersed is contained in the steel, thereby inducing martensite transformation at room temperature to ensure high strength and high ductility.

Thus, the TRIP high-strength steel contains Si and Mn as a steel component in an amount of 1-2 wt%. These Si and Mn act as nuclei for oxide formation during annealing and form Si and Mn oxide films on the steel surface, It is known as a nondissolving component which worsens the wettability with molten zinc. As a result, it is difficult to secure the adhesion of plating, and bare spots are generated. In addition, since the interfacial inhibition layer, that is, Fe ₂ Al ₅ and FeAl _{3, which} are Fe-Al intermetallic compounds, are not uniformly formed at the interface between the plating layer and the substrate layer, the plating adhesion is deteriorated, Plating peeling occurs, and it becomes difficult to secure workability.

Various techniques have been proposed in order to solve such Zn-based hot dip galvanizing.

For example, Japanese Patent Application Laid-Open No. 2000-239788 discloses, the addition of Ni or Zr suppresses the formation of Si oxide in the steel and by reducing the surface concentrated layer of _{SiO 2, Mn 2 SiO 4,} MnSiO 3 coated Suggesting ways to improve gender. However, the above method has a problem that the manufacturing cost is increased due to the addition of expensive Ni, Zr or the like in the steel.

As another method, Japanese Patent Application Laid-Open No. 2001-279409 discloses a technique for improving the plating ability by forming an iron oxide film of 50-1000 nm in thickness on the surface of a high tensile steel sheet by electroplating to suppress the concentration of Si and Mn Lt; / RTI > However, in the technique disclosed in the above patent documents, it is necessary to additionally install an electroplating facility for lead plating. When the thickness of an oxide film such as Fe or Ni formed by electroplating is thin or not uniform, There is a disadvantage that the oxide does not rise to the surface layer and the hot dip galvanizing property can not be improved.

In another method, Japanese Patent Application Laid-Open No. 2007-308261 discloses a method of suppressing the surface layer distribution of Si and Mn oxide by performing heat treatment in an oxidizing atmosphere using an oxidation-reduction method to form an oxide of Fe and then reducing in a reducing atmosphere . However, in the technique disclosed in the above patent documents, when the thickness of the Fe oxide formed by the oxidation heat treatment is thin, Si and Mn diffuse into the surface layer through the Fe oxide layer during the reduction process to form Si and Mn oxide, When the thickness of the FeO oxide layer is large, all the FeO oxides can not be reduced during the reduction process, resulting in a problem of deteriorating the hot dip galvanizing property. Further, Si and Mn-based oxides are formed in the form of stripes on the Fe oxide layer and the base layer interface, and plating peeling may occur at the interface portion at the time of processing. Therefore, it is required to strictly control the thickness of the FeO layer produced in an oxidizing atmosphere.

As described above, various methods have been developed for the production of high strength Zn-Al-Mg alloy hot dip galvanized steel sheet excellent in plating adhesion, but all of the techniques disclosed in these prior art documents have found that the surface diffusion of Si and Mn- As an indirect method to prevent, it is not a method to remove Si and Mn oxide fundamentally.

As another method, Japanese Patent Application Laid-Open No. 2003-056901 discloses a method of plating after plating after chemical annealing after annealing, removing oxide scale using Si or Mn oxide with hydrochloric acid or sulfuric acid. However, in this case, there are various problems such as corrosion of equipment and difficulty of picking up acid by using strong acid such as hydrochloric acid or sulfuric acid.

The Si, Mn-based oxide layer formed on the surface after the annealing heat treatment is a fundamental cause of deterioration in wettability of hot dip galvanizing and deterioration of uncoated and plating adhesion after hot dip galvanizing.

Accordingly, it is an object of the present invention to provide a high strength Zn-Al-Mg alloy hot-dip galvanized steel sheet free from unplated and excellent plating adhesion by removing Si and Mn based oxides formed on the surface after annealing heat treatment, and a method of manufacturing the same. .

The present invention relates to a method of manufacturing a hot-dip Zn-Al-Mg alloy hot dip galvanized steel sheet which is free of unplated and excellent plating adhesion by removing Si and Mn-based oxides formed on the surface after annealing heat treatment. , A cold annealing step of annealing a cold-rolled steel sheet containing 0.05 to 0.3% by weight of C, 0.5 to 2.0% by weight of Si and 0.5 to 3.0% by weight of Mn at a temperature of 700 ° C to 900 ° C and cooling the annealed annealed steel sheet, A shot blasting step of spraying a short ball on the surface of the steel sheet to remove oxides on the surface of the steel sheet, and a step of dipping the oxide-removed cold-rolled steel sheet in a Zn-Al-Mg hot dip galvanizing bath at 420 ~ The present invention also provides a method of manufacturing a Zn-Al-Mg hot-dip galvanized steel sheet,

Preferably, the shotblasting step is performed such that the average surface roughness of the surface of the steel sheet from which the oxide is removed is in the range of 0.5-3.0 m, and the shotblasting step is performed at a speed of 40-78 m / sec At a speed of < / RTI >

The Zn-Al-Mg hot dip galvanizing bath preferably contains 1-15% by weight of Al and 1-4% by weight of Mg and the balance of zinc and unavoidable impurities. The Zn-Al-Mg hot- The abstinence may be at a temperature of 430-500 < 0 > C.

According to an embodiment of the present invention, there is provided a high strength Zn-Al-Mg alloy hot-dip galvanized steel sheet which is free of unplated and excellent in plating adhesion, and which comprises 0.05-0.3% by weight of C, 0.5-2.0% And 0.5 to 3.0% by weight of Mn; And a Zn-Al-Mg hot dip galvanized steel sheet having an average surface roughness of 0.5-3.0 m on the surface of the steel sheet.

The hot dip galvanized layer preferably contains 1-15% by weight of Al and 1-4% by weight of Mg and the balance of zinc and unavoidable impurities.

By the removal of Si and Mn oxide by the method of the present invention, good wettability of hot dip galvanizing can be ensured, thereby preventing occurrence of unplated. Further, by adjusting the average surface roughness of the steel sheet, the wettability can be improved, and the plating adhesion to the surface of the steel sheet can be improved.

Further, a high-quality, high-strength, pervapored Zn-Al-Mg alloy hot-dip galvanized steel sheet having excellent plating adhesion can be obtained.

1 is a schematic view showing a process for manufacturing a high strength Zn-Al-Mg hot-dip galvanized steel sheet according to the present invention.

Hereinafter, the present invention will be described in detail.

The present invention relates to a hot-dip Zn-Al-Mg alloy hot-dip galvanized steel sheet excellent in plating adhesion and a method for producing the same, and more particularly, Zn-Al-Mg-based hot-dip galvanized steel sheet which is free from unplated and has excellent plating adhesion, by fundamentally cutting off the source of Si and Mn-based annealed oxides resulting in the occurrence of Si-Mn-based annealed oxides.

The present invention can be applied to a cold-rolled steel sheet containing Si and Mn, in which an oxide film is formed on the surface of a steel sheet by Si and Mn during the annealing heat treatment process to lower the plating adhesion of hot-dip galvanizing. The composition of the steel sheet is not particularly limited and may be, for example, 0.05 to 0.3% by weight of C, 0.5 to 2.0% by weight of Si and 0.5 to 3.0% by weight of Mn, the remainder being Fe and other inevitable impurities, It can be more suitably applied to steel sheets. The reason why the composition of the steel sheet for galvanizing is limited as described above will be described in more detail below.

C: 0.05 to 0.3 wt%

C is an austenite stabilizing element and moves from the ferrite in the bimetallic transformation temperature region and the bimetallic coexistence temperature region and is concentrated to the austenite. As a result, even if the steel sheet is cooled to room temperature, the stabilized austenite can remain at a level of 2 to 20%, thereby securing the formability due to transformational organic firing.

For this, the steel sheet preferably contains C in a range of 0.05 to 0.3% by weight. When C is less than 0.05% by weight, it is difficult to secure a retained austenite structure of 2% or more. On the other hand, when C is added in an amount exceeding 0.3%, weldability deteriorates.

Si: 0.5 to 2.0 wt%

Si is not dissolved in cementite and inhibits the precipitation of cementite, thereby delaying the transformation from austenite at a temperature of 350 to 600 ° C. Therefore, it is possible to accelerate the concentration of C in the austenite, thereby improving the chemical stability of the austenite and securing the retained austenite which causes transformational organic firing and improves the formability.

If the Si content is less than 0.5% by weight, the above-mentioned effect can not be sufficiently obtained. If the Si content is more than 2.0% by weight, the steel properties become brittle, which is not preferable. Therefore, the addition amount of Si is more preferably limited to the above range.

Mn: 0.5 to 3.0 wt%

Mn is an element promoting austenite formation and prevents austenite from being decomposed into pearlite during cooling to 350 to 600 ° C after annealing in the coexistence temperature region of two phases so that austenite remains in the metal structure during cooling to room temperature .

Therefore, in the present invention, 0.5 wt% or more of the austenite is added to suppress residual austenite and transformation into pearlite. When the content exceeds 3.0 wt%, the band structure is increased to deteriorate the physical properties.

In addition, the steel sheet of the present invention contains iron and unavoidable impurities. However, other than C, Si and Mn, there is no particular influence on the plating performance, so the content of the other components is not particularly limited in the present invention.

According to an embodiment of the present invention, a cold-rolled steel sheet as described above is subjected to a first reduction heating, a shot blasting, a second reduction heating and a hot-dip galvanizing step to obtain a hot-dip galvanized steel sheet. A process for producing such a hot-dip galvanized steel sheet is schematically shown in FIG. 1, and a method for manufacturing a hot-dip galvanized steel sheet according to the present invention will be described below with reference to FIG.

As shown in Fig. 1, lubricating oil or the like adhering to the surface of the steel sheet is degreased in the degreasing tank 1, and the cold-rolled steel sheet is annealed in the annealing furnace 3. The annealing temperature in the annealing furnace 3 is not particularly limited and can be carried out in a temperature range in which it is usually carried out. For example, it is preferable to heat the annealing furnace at a bimetallic temperature of 700 to 900 ° C.

The atmosphere of the annealing furnace 3 is not particularly limited and can be performed in a reducing atmosphere that is usually applied. The reducing atmosphere includes, for example, 5 to 10% of H ₂ and 90 to 95% of N ₂ , and the dew point can be performed at -20 ° C to -60 ° C.

Generally, after the above annealing treatment, the steel sheet is cooled to about 430 to 500 ° C by air or high-hydrogen cooling, and then a hot dip galvanizing process is performed. During the annealing process, Si and Mn contained in the steel are diffused into the surface layer, and oxides such as SiO ₂ , Fe ₂ SiO ₄ , Mn ₂ SiO ₄ and MnSiO ₃ are concentrated on the surface of the steel sheet. As described above, when Si and Mn-based oxides are concentrated on the surface of the steel sheet to form an oxide layer, the wettability of molten zinc to the surface of the steel sheet in the hot-dip galvanizing step after annealing is lowered. Therefore, when Zn-Al-Mg alloy hot dip galvanizing is performed in the state where Si, Mn-based oxides are formed on the surface, a large amount of bare spots is generated and a rain mark is formed, Resulting in surface defects.

Accordingly, in order to remove Si and Mn oxides concentrated in the surface layer of the steel sheet after annealing and cooling in the annealing furnace 3, the steel sheet is shot blasted by the shot blasting chamber 5 to remove Si, Mn-based oxides .

In the shot blasting process, most of the concentrated Si and Mn oxides existing on the surface of the steel sheet can be removed by uniformly spraying the short balls in the width direction on the surface of the cold-rolled steel sheet having a flat shape. Further, by accelerating the cracking of the Si and Mn oxide layers concentrated in the surface layer of the steel sheet by shot blasting to improve the reactivity of the molten amount to the base steel sheet, the Zn-Al-Mg alloy to the steel sheet also accelerates the reactivity of the alloy And it is possible to suppress occurrence of unplated defects due to such oxide layers in the molten gold plating process.

Further, the surface roughness of the steel sheet can be imparted by performing a shot blasting treatment on the surface of the steel sheet. Such surface roughness can improve the wettability of the plating solution in the plating step and improve the plating adhesion.

Here, the shot blasting may be a short ball having a diameter of 0.3 to 0.8 mm although it may vary depending on the surface roughness formed on the surface of the steel sheet. When the diameter of the short ball is less than 0.3 mm, the oxide removal efficiency is lowered, and when the diameter is more than 0.8 mm, the roughness may become larger. When a low surface roughness is required, a shot ball having a diameter of 0.3 to 0.6 mm can be used.

It is also preferable to spray the shot ball at a speed of 40 to 78 m / sec in order to remove the Si and Mn oxides concentrated on the surface of the steel sheet and to form the surface roughness. At this time, when the injection speed is high, the amount of impact increases, so that the removal of the oxide is easy, but the surface roughness formed on the steel sheet is increased. When the injection speed is low, the oxide removal efficiency is lowered. The jetting speed can be controlled by controlling the blasting wheel speed, and may be varied depending on the mechanical characteristics, but it can be adjusted by controlling the blasting wheel speed usually at 1200 to 2100 rpm.

In this case, the injection amount of the short ball is preferably controlled to 800 kg / min or more in order to efficiently remove the oxide layer on the surface of the steel sheet by shot blasting. However, in the case of exceeding 1300 kg / min, it is preferable to spray at a range of 800-1300 kg / min, which may put burden on the equipment.

The shot blasting may be carried out by a single shot blasting chamber 5, or a plurality of shot blasting chambers 5 may be used, for example, two to six shot blasting chambers 5 depending on the line speed of the cold-rolled steel strip.

As described above, the surface roughness of the steel sheet can be adjusted according to the shot blasting injection condition, and the irregularities generated on the surface of the steel sheet by the impact of the shot ball increase the adhesion strength between Fe and the Zn-Al-Mg plating layer of the steel sheet . For this purpose, the surface roughness Ra of the cold-rolled steel sheet after shot blasting is preferably in the range of 0.5 to 3.0 탆. When the surface average roughness is less than 0.5 탆, the surface is too flat and the wettability of the molten zinc is not good and flows down. When the surface average roughness exceeds 3.0 탆, the irregularities of the steel sheet are too severe, Unevenness may remain on the surface to deteriorate the surface quality of the steel sheet and may deteriorate workability such as peeling of the plating layer during bending processing.

After removing the Si and Mn-based oxide layer through the shot blasting process, the steel strip is degreased by a second degreasing bath 7 as required, and then a second reduction process is performed. The reducing furnace 9 is not particularly limited as long as it can be performed in a typical reducing atmosphere. For example, as in the above annealing step, the reducing furnace 9 is made of a mixture of 90 to 95% of nitrogen, 5 to 10% of hydrogen, Lt; 0 > C to -60 < 0 > C.

However, the reduction process stabilizes the retained austenite and raises the cold-rolled steel strip to a temperature suitable for hot-dip galvanizing, and is preferably performed by heating the steel sheet in the temperature range of 420 to 550 ° C. Since the temperature of the reducing furnace 9 should be a temperature at which the surface layer diffusion of Si and Mn can be minimized, it is preferable that the temperature of the steel sheet does not exceed 550 deg. Further, in order to perform the alloy hot-dip coating, a temperature similar to the melting point of Zn-Al-Mg hot-dip zinc is required at least, so that the steel sheet heating temperature is preferably 420 ° C or higher.

The molten zinc alloy plating may be performed by immersing the treated steel sheet in a hot-dip galvanizing bath 11 carrying a plating bath at a temperature ranging from 430 to 500 ° C. The plating bath is not particularly limited, but usually a plating bath having a composition used in the production of a Zn-Al-Mg alloy cold rolled hot dip galvanized steel sheet can be applied. For example, 1 to 15% 1 to 4% by weight, and the balance of zinc and unavoidable impurities.

Since the Si and Mn-based oxides can be minimized from the surface layer of the steel sheet immediately before the cold-rolled steel sheet is introduced into the hot-dip galvanizing bath by the above-described method of the present invention, the Fe of the steel sheet and the Zn- It is possible to produce a hot-dip galvanized steel sheet excellent in wettability and excellent in adhesion between the base steel sheet and the plating layer.

Example

Hereinafter, the present invention will be described in more detail with reference to examples. The following examples are only illustrative of one embodiment of the present invention, and the present invention is not limited thereto.

Example  1 to 5 and Comparative Example  1-5

A 590 MPa grade modified organic-sintered steel containing 0.09% by weight of C, 1.2% by weight of Si and 1.7% by weight of Mn in the steel was used as a test material.

The degreased treated modified organic plastic steel sheet was placed in a reducing furnace at a temperature of -60 캜 maintained at a dew point temperature of -60 캜 in a reducing atmosphere of 5% of H ₂ and 95% of N ₂ , and was annealed for 30 seconds, And cooled to 25 DEG C at a cooling rate. As a result, the surface of the annealed steel sheet was observed, and it was confirmed that Si and Mn were concentrated in the surface layer portion of the steel sheet to form an oxide layer of 0.5 mu m formed thereon.

The surface of the annealed steel sheet was subjected to shot blasting. At this time, the shot blasting process was performed by varying the size and type of the shot ball and the speed of the blade wheel as shown in Table 1.

The presence or absence of Si and Mn oxide layers was observed on the surface of the shot blast-treated steel sheet, and the average surface roughness (Ra) was measured. The results are shown in Table 1. The average surface roughness (Ra) was measured on a three-dimensional surface-type measurement area of 3.5 mm x 4.7 mm to obtain an average surface roughness.

The steel sheet subjected to the short-blasting treatment was washed with water and then put in a reducing furnace of 400 ° C maintained at a reducing atmosphere of 5% H ₂ and 95% N ₂ and at a dew point temperature of -60 ° C and held for 30 seconds for reduction treatment.

The steel sheet subjected to reduction treatment was subjected to hot dip galvanizing at 450 DEG C containing 2.5% by weight of Al, 3% by weight of Mg and residual zinc and other inevitable impurities. At this time, the drawing temperature of the steel sheet was 440 DEG C, and the coated steel sheet was plated so as to have a plating amount of 60 g / m < 2 > on one side to obtain a zinc alloy-plated steel sheet of Zn-Al-Mg.

Comparative Example  6

A Zn-Al-Mg hot dip galvanized steel sheet was produced in the same manner as in Example 1, except that the shot blasting treatment was not performed.

[evaluation]

The plating quality of the thus obtained coated steel sheet was observed and evaluated as follows, and the results are shown in Table 1.

[Plating quality]

The surface appearance was visually observed and the quality of the plating was evaluated according to the amount of unplated generation. The evaluation criteria were as follows.

1: Plating occurrence area 0%

2: Less than 0.1% of the occurrence area of unplated, uncoated size of 0.1 mm or less

3: Unplated area less than 0.1-0.3%, uncoated 0.5mm or less

4: Less than 0.3-0.5% of plated area, uncoated 1mm or less

5: Unplated area over 0.5%, unplated size exceeding 1mm

[Plating adhesion]

Zn-Al-Mg alloy The plating adhesion was observed according to whether the plating layer was peeled off when each plated test piece was bent at 180 °.

Distinction Short ball
size
(탆) Blasting Wheel Rotation Speed
(rpm) Short ball
Injection speed
(m / sec) Short ball
Injection quantity
(kg / min) Presence or absence of oxide layer Average
Surface roughness
Ra (탆) Plating quality Plated
Adhesiveness Comparative Example 1 100 900 28 900 U 0.3 3 Exfoliation Comparative Example 2 200 900 28 500 U 0.4 2 Exfoliation Inventory 1 300 1200 40 1200 radish 0.8 One Peeling off Inventory 2 300 1300 44 1200 radish 1.1 One Peeling off Inventory 3 500 1500 52 1300 radish 1.4 One Peeling off Honorable 4 500 1600 57 1300 radish 1.5 One Peeling off Comparative Example 3 800 900 28 900 U 0.7 3 Exfoliation Inventory 5 800 1600 57 1300 radish 2.5 One Peeling off Comparative Example 4 1000 2000 73 1300 radish 3.1 One Exfoliation Comparative Example 5 1000 2300 86 1300 radish 3.7 One Exfoliation Comparative Example 6 - - - - U 0.3 5 Exfoliation

As can be seen from Table 1, the short ball at the time of short blasting after the first annealing was set to 0.3 to 0.8 mm, the shot speed of the shot ball was set at 40-78 m / sec (shot blasting wheel rotation speed 1200 to 2100 rpm) Examples 1 to 5, which were controlled and treated, effectively produced a Zn-Al-Mg alloy plated steel sheet which was effectively removed from the surface of the steel sheet and the Si and Mn oxides were not removed, I could.

However, as can be seen from Comparative Examples 1 to 5, when the size of the shot ball and the rotation speed of the shot blasting wheel were deviated from the above conditions, unplated or plating peeling was observed. In the case of the coated steel sheet not subjected to shot blasting, the Si and Mn annealed oxides were present on the surface of the steel sheet, and the plating wettability was not secured.

1: First degreasing bath 3: Annealing furnace
5: shot blasting 7: second degreasing tank
9: Reduction furnace 11: Hot-dip galvanizing bath
13: Gas Wiping

Claims (7)

Annealing a steel sheet containing 0.05 to 0.3% by weight of C, 0.5 to 2.0% by weight of Si and 0.5 to 3.0% by weight of Mn at a temperature of 700 to 900 캜 for cooling and annealing;
A shot blasting step of spraying a short ball on the surface of the heat-treated cold-rolled steel sheet to remove oxides on the surface of the steel sheet; And
A hot-dip coating process in which the cold-rolled steel sheet from which the oxides have been removed is subjected to a second heat treatment at 420 to 550 ° C and dipped in a Zn-Al-Mg hot dip galvanizing bath to perform plating
Zn-Al-Mg hot-dip galvanized steel sheet.
The zinc-coated hot-dip galvanized steel sheet manufacturing method according to claim 1, wherein the shot blasting is performed so that an average surface roughness of the surface of the steel sheet from which the oxide is removed is in the range of 0.5-3.0 m.
2. The method of claim 1, wherein the shot blasting step comprises spraying a shot ball having a diameter of 0.3 to 0.8 mm at an injection speed of 40 to 78 m / s.
The method of claim 1, wherein the Zn-Al-Mg hot dip galvanizing bath comprises Zn-Al-Mg, wherein the Zn-Al-Mg hot dip galvanizing bath comprises 1-15 wt.% Al and 1-4 wt.% Mg and the balance comprises zinc and unavoidable impurities. A method for manufacturing a hot dip galvanized steel sheet.
5. The method of claim 4, wherein the Zn-Al-Mg hot dip galvanizing bath has a temperature of 430-500 [deg.] C.
0.05 to 0.3% by weight of C, 0.5 to 2.0% by weight of Si and 0.5 to 3.0% by weight of Mn; And a Zn-Al-Mg hot-dip galvanized steel sheet on the surface of the cold-rolled steel sheet, the Zn-Al-Mg hot-dip galvanized steel sheet having an average surface roughness of 0.5-3.0 m on the steel sheet surface.
7. The Zn-Al-Mg hot-dip galvanized steel sheet according to claim 6, wherein the hot-dip galvanized layer contains 1-15% by weight of Al and 1-4% by weight of Mg, and the balance of zinc and unavoidable impurities.

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