JPH1136057A - Fine spangle hot-dip galvanized steel sheet and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a hot-dip Zn-Al series alloy plated steel sheet good in formability and workability and excellent in designing properties with fine spangles by regulating the concn. of Si in plating coating in the region excepting an alloy layer present on the boundary of the plating-steel sheet and furthermore regulating the average spangle diameter in the surface of the coating to specified value or below. SOLUTION: This plated steel sheet has the average plating coating contg., by weight, 40 to 70% Al and 0.5 to 2.0% Si, and the balance Zn. Then, the concn. of Si in the plating coating in the region excepting an alloy layer present on the boundary of the plating-steel sheet is <=1 wt.% and lower than the concn. of Si in the average plating coating, and moreover, the average spangle diameter in the surface of the plating coating is regulated to <=0.7 mm. For obtaining the plated steel sheet, the steel sheet annealed at 650 to 690 deg.C is applied with hot-dip plating in a hot-dip Zn-Al series plating bath having a compsn. same as the above and contg. Al and Si.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-treated steel sheet used for home appliances, building materials, automobiles and the like, and a method for producing the same.
The present invention relates to a system alloy-plated steel sheet and a method for producing the same.

[0002]

2. Description of the Related Art Hot-dip Zn-Al alloy plating is applied to improve the corrosion resistance and weather resistance of steel sheets.
In recent years, the application amount has increased. A typical example is a hot-dip aluminum-zinc alloy-coated steel sheet, for example, 4 to 75% by weight of aluminum with the balance being Zn, and Si, Mg, Ce-La.
There is an aluminum-zinc alloy-plated steel sheet plated with an alloy containing a small amount of a third component such as the above.

[0003] Currently, 4 to 10% by weight of aluminum is commercialized, most of which is zinc and trace amounts of aluminum.
Low aluminum-zinc alloy coated steel sheet plated with an alloy containing Mg or Ce-La, and high aluminum-zinc alloy plating with an alloy containing 55% by weight of aluminum, 43.4% by weight of zinc and 1.6% of Si There are two types of steel plates.

[0004] With regard to corrosion resistance, 1.5 to 2 times the low aluminum-zinc alloy coated steel sheet and 3 to 6 times the high aluminum-zinc alloy coated steel sheet as compared with the conventional hot-dip galvanized steel sheet. It has excellent properties. Moreover, the high aluminum-zinc alloy plated steel sheet is also excellent in heat resistance and heat reflectivity.

[0005] As described above, aluminum-zinc alloy-plated steel sheets have attracted special attention recently because of their excellent properties, and are used for construction materials such as roofing materials and wall materials, guard rails, wiring piping, support frames, soundproof walls, and drainage trenches. It is rapidly spreading as a material for products, a home appliance such as a dryer and a microwave oven, a material for industrial equipment, and a substrate for a coated steel plate.

[0006] Above all, Zn-55% Al alloy-plated steel sheet is a high-performance plated steel sheet having both the durability, heat resistance and heat reflection property of aluminum and the sacrificial corrosion resistance of zinc. Widely used for automotive parts. This plated steel sheet is typically made of Al: 55% by weight.
%, Zn: 43.4%, and Si: 1.6%. The ratio of Al and Zn is determined in consideration of corrosion resistance, and Si is added to suppress an alloy reaction with a steel substrate that inhibits plating adhesion.

[0007] Unlike other Zn-Al alloy-plated steel sheets having a low Al content, this Zn-55% Al alloy-plated steel sheet has a characteristic silver-white spangle pattern on the plating surface, and is made of fabric due to its design. As it is, it is widely used for roofs and walls of commercial and industrial buildings and general-purpose buildings, or for objects.

[0008] The particle size of spangles on the plating surface of a Zn-55% Al alloy-plated steel sheet varies depending on the hot-dip coating conditions, particularly the solidification rate of the hot-dip coating after hot-dip coating, but is generally about 0.8 mm or more on average. Thus, the spangle pattern can be visually identified. However, in some applications, spangle patterns cannot be visually identified, that is, micro spangles having an average spangle particle size of 0.7 mm or less (minimum spangle or zero spangle) are preferred.

In general, it is known that the spangle particle size of a hot-dip coated steel sheet decreases when the cooling rate (and, consequently, the solidification rate of a plating film) is increased by increasing the air volume during forced cooling after hot-dip coating. However, it is difficult to stably reduce the average spangle particle size of the Zn-55% Al alloy-plated steel sheet to less than 0.8 mm even when the steel sheet is rapidly cooled after the plating. In addition, rapid cooling increases the residual stress in the plating film, makes the plating film brittle and reduces its workability. In addition, the rapid cooling of the base steel sheet itself causes an increase in hardening and aging deterioration. Properties and processability are adversely affected.

Regarding spangles of hot-dip coated steel sheets,
It has also been practiced to eliminate the spangle pattern by performing skin pass reduction after the plating film has solidified. However, if this method alone is used to eliminate the spangle, the appearance deterioration due to the remaining spangle and the uneven appearance after painting are likely to occur. Also,
There is also a problem that the plating film is easily picked up by the skin pass roll, so that flaws are likely to occur, and a spangle pattern tends to emerge during press working by the user.

Further, a technique of spraying solid or liquid fine particles onto an unsolidified plating surface of a hot-dip coated steel sheet immediately after plating to uniformly generate a large number of solidification nuclei and rapidly cooling the same to make spangles finer. (See, for example, Japanese Patent Application Laid-Open Nos. 50-38638, 63-143249, and 63-153255 for hot-dip aluminized steel sheets).

By adopting this method, it is possible to make the average spangle diameter of the plating surface of the Zn-55% Al alloy plated steel sheet smaller than 0.8 mm. Problems such as aging deterioration of the base material itself cannot be solved yet. In addition, this method requires the addition of a fine particle spraying device to a conventional hot-dip plating facility,
Increases cost.

Japanese Patent Application Laid-Open No. 59-56570 discloses that molten Zn having a very fine spangle and excellent corrosion resistance, which comprises adding 3 to 20% by weight of Mg together with 3 to 15% by weight of Si in a plating bath. -Al alloy plated steel sheet is described. However, since a relatively large amount of Si and Mg coexist in the plating film, this plated steel sheet has a problem that workability is deteriorated due to precipitation of Si and Mg in the film.

Further, JP-A-8-49055 discloses that A
l: 20 to 80 wt%, Si: 0.1 to 2.0 wt%, and 0.001 to 0.5 wt% of Ti contained in a plating bath consisting of a residual amount of Zn. Can be formed. However, when Ti is added, dross is generated in the plating bath, which reduces not only the plating workability but also the corrosion resistance of the plating film.

[0015]

SUMMARY OF THE INVENTION An object of the present invention is to provide a plating film having good formability and workability and a fine spangle design without the presence of other elements such as Mg and Ti. It is an object of the present invention to provide a hot-dip Zn-Al alloy-plated steel sheet excellent in quality and a method for producing the same.

[0016] Another object of the present invention is to provide an aluminum-killed cold-rolled steel sheet without spraying fine particles that impair the formability and workability of the plating film and the steel sheet and that require a change in the existing hot-dip coating equipment. Another object of the present invention is to provide a hot-dip Zn-Al alloy-plated steel sheet having a hot-dip Zn-Al alloy-plated film having a fine spangle and a method for producing the same.

[0017]

SUMMARY OF THE INVENTION Hot-dip Zn-Al alloy-coated steel sheets are generally produced by conventional continuous hot-dip galvanizing equipment such as those used for hot-dip galvanizing. In a typical continuous hot-dip coating equipment, a base material steel sheet (cold-rolled steel sheet or hot-rolled steel sheet) annealed in a continuous annealing furnace is immersed in a hot-dip plating bath via a snout without exposure to the atmosphere, and then exits the plating bath. Immediately after controlling the coating weight to the desired amount by gas wiping, the temperature at which solidification is completed in the cooling zone (usually air cooling)
(Approximately 370 ° C. for Zn-55% Al alloy plating) After cooling to below, lightly press down with a leveler or skin pass roll if necessary and wind up.

The present inventors have conducted intensive studies on means for minimizing spangles of a hot-dip Zn—Al alloy plating film by directly using such conventional plating equipment.
After hot-rolling and cold-rolling the killed steel, the resulting cold-rolled steel sheet is used as a base material, continuously annealed, and then hot-dip in an Al-Zn alloy molten bath with an adjusted Si content. The present inventors have found that a plating film having a fine spangle having an average spangle particle size of 0.7 mm or less can be formed, and the present invention has been completed.

That is, the average spangle on the plating surface is controlled by controlling the alloy layer at the interface between the plating and the steel sheet, that is, by setting the Si content of the portion excluding the alloy layer existing at the interface between the plating and the steel sheet from the plating film to 1% or less. A hot-dip Zn-Al-based alloy plated steel sheet having a plating surface with a grain size of 0.7 mm or less is obtained.

Here, the present invention relates to the case where Al: 40 to 70 wt% and S
i: a hot-dip Zn-Al-based alloy-coated steel sheet containing 0.5 to 2.0 wt% and having an average plating film composition consisting of the balance of Zn, and excluding the alloy layer existing at the plating-steel interface. A molten Zn-Al based alloy having minute spangles, wherein the Si concentration is 1 wt% or less, the Si concentration of the average plating film composition is lower, and the average spangle diameter of the plating film surface is 0.7 mm or less. It is a plated steel sheet.

In an embodiment of the present invention, the plating film composition may further contain at least one selected from the group consisting of Zr, Hf and V in an amount of 0.01 to 0.4 wt%.

From another aspect, the invention relates to a method for annealing at an annealing temperature of 650-69.
Al: 40-70wt%, Si: 0.5%
Si concentration of the plating film in a region excluding the alloy layer existing at the plating-steel plate interface, characterized in that immersion plating is performed in a molten Zn-Al-based alloy plating bath having a composition of up to 2.0 wt% and the balance being Zn. Is less than 1 wt%, and Si of the plating bath is
Molten Zn-Al with a small spangle whose concentration is lower than the concentration and the average spangle diameter of the plating film surface is 0.7 mm or less
This is a method for producing a base alloy plated steel sheet.

In an embodiment of the present invention, the plating bath may further contain at least one selected from the group consisting of Zr, Hf and V in an amount of 0.01 to 0.4 wt% each. Further, in an embodiment of the present invention, the alloy layer has a Si content of 1.5 to 20%, and the alloy layer has an adhesion amount of 3 to 3%.
６6 g / m ² .

[0024]

Next, the present invention will be described in detail. In this specification, "%" is wt% unless otherwise specified.

(Plating Film and Bath Composition)
Al: 40 to 70% and Si: 0.5 to 2.0%. If desired, one or two of Zr, Hf, V may be further added to the plating bath.
More than one species may be contained in each of 0.01 to 0.4%. The balance of the plating bath is zinc and unavoidable impurities. The composition of the plating film is substantially the same as the composition of the plating bath.
However, in the case of the present invention, in the region other than the alloy layer, the Si concentration is different from the Si concentration of the bath composition, and therefore the composition of the entire plating film is referred to as “average plating film composition” for convenience. In the prior art, unless there is a special reason, the formation of this alloy layer is as small as possible. Therefore, it can be said that the composition of the plating film is substantially the same as the composition of the plating bath.

Al content is 40-70%, preferably 50-60%
And If the Al content is less than 40%, the melting temperature of the bath decreases and the solidification start temperature of the plating film becomes 500 ° C or less, so the time until solidification is completed increases, the spangle diameter increases, and the average is 0.7 mm. It is difficult to have the following spangle diameter. In addition, since the Zn content in the film relatively increases, the Al dendrite phase forming spangles decreases, the spangles themselves become unclear, and the beautiful spangles provided by the fine spangles aimed at in the present invention. Appearance,
That is, the desired design property cannot be obtained. Further, the Zn-rich phase in the plating layer increases, and the corrosion resistance deteriorates due to the promotion of intergranular corrosion and the promotion of selective corrosion. On the other hand, when the Al content exceeds 70%, the Al-rich phase increases, so that the sacrificial corrosion resistance of Zn decreases, and the corrosion resistance decreases again.

Si: Si has been conventionally used to suppress the development of a brittle Fe-Al alloy layer formed at the plating film-base metal interface.
-Has been added to Al alloy plating baths. As previously mentioned,
In the hot-dip plating of Zn-55% Al alloy, about 1.6% of Si is usually contained for this purpose. In the present invention, in view of the alloy layer described later, the Si-
The content is 0.5 to 2.0%, preferably 0.7 to 1.2%.

The average plating film composition of the plating film is the same as that of the plating bath, but the Si concentration of the plating film excluding the alloy layer is 1% or less as described later. This ensures that the average spangle diameter is 0 by ensuring a sufficient solidification rate.
This is to make it 7 mm or less.

Zr, Hf, V: These elements are optionally used to further improve the workability of the plating film.
It may be contained in the Al alloy plating film. Improvement in workability is achieved by dispersing the additive elements uniformly in the plating film, spheroidizing Si precipitated in the film, and relieving stress concentration in the plating film during processing.

In the case where these elements are added, each is added in an amount of 0.1.
It is contained in an amount ranging from 01 to 0.4%, preferably from 0.05 to 0.2%. If the addition amount is less than 0.01%, the effect of homogenization of the film by uniform dispersion is small, and if it exceeds 0.4%,
Not only does the effect of film homogenization become saturated, but also the amount of dross generated from the plating bath during operation increases, leading to deterioration in plating quality and cost.

Alloy layer: The alloy layer formed at the interface between the plating and the steel sheet is usually composed of three elements of Fe-Al-Si, and is θ, τ ₅ , τ ₆ and Si in order of decreasing Si concentration. The respective stoichiometric compositions are as shown in Table 1.

The present inventors have examined the relationship between the composition of the alloy layer and the film thickness in detail, and have found the following relationship. That is, the alloy layer formed by a change such as an increase in Si in the bath changes from θ to τ ₅ and τ ₆ , and the Si layer in the alloy layer
The concentration is higher.

On the other hand, the Si concentration in the bath increases,
As the Si concentration increases, the reaction with Fe is suppressed, so that the thickness decreases. The total amount of Si in the alloy layer is represented by the product of these.

Further, since the formation rate of the alloy layer is affected by the degree of activation of the steel sheet surface by the annealing treatment as a pre-treatment before plating, the thickness of the obtained alloy layer depends on such activity of the steel sheet surface. It is also affected by the degree of conversion, specifically the annealing temperature. That is, bath temperature,
Processing conditions such as the temperature of the steel sheet and the annealing temperature, particularly the annealing temperature, affect the thickness of the alloy layer and thus the amount of Si in the alloy layer.

From the above, the Si concentration in the melt in the remaining region of the plating film other than the alloy layer (hereinafter, also simply referred to as the remaining Si concentration) is determined by the thickness of the alloy layer and its Si amount.

The spangle diameter is determined by the solidification of the melt after the formation of the alloy layer. Therefore, by controlling the composition and thickness of the alloy layer, the remaining molten Si, ie, the amount of the remaining Si, is limited to a certain value or less. The spangle diameter can be controlled. This is expressed by the following equation.

Residual Si content (%) = [(bath Si content (%) × plated amount) − (alloy layer Si content (%) × alloy layer deposited amount)] / (plating deposited amount−alloy layer deposited Amount) ≦ 1.0 (%) Therefore, in order to reduce the spangle particle size, that is, to increase the solidification speed, the driving force at the time of solidification may be increased. For this purpose, the difference between the liquid phase equilibrium Si concentration at the solid-liquid interface and the liquid phase bulk Si concentration may be increased. In other words, it is considered that the lower the Si concentration in the remaining melt after the alloy phase is formed, the higher the solidification rate and the smaller the spangle particle size.

The inventors of the present invention have conducted intensive studies. As a result, if the Si concentration in the remaining molten liquid is set to 1% by weight or less, the molten Zn-Al having a plating surface having an average spangle particle size of 0.7 mm or less on the plating surface is obtained. It has been found that a base alloy plated steel sheet can be obtained.

In order to reduce the Si concentration in the remaining molten liquid to 1% by weight or less, for example, by setting the annealing temperature to 650 to 690 ° C. and setting the Si concentration in the plating solution to 0.5 to 2.0%, an appropriate alloy layer is formed. May be generated in an appropriate amount. Speaking of the Si concentration during plating, it is preferably 0.7 to 1.
2%.

In the present invention, the Si content of the alloy layer is generally in the range of 1.5 to 20%, and the amount of the deposited alloy layer is 3 to 6 g / m ² . Preferably, each 2-16%,
It is 3 to 5 g / m ² . More preferred ranges are 2 to 2, respectively.
8%, which is 3.5 ~5g / m ^2.

[0041]

[Table 1]

(Spangle Diameter) In the present invention, the spangle diameter is measured by measuring the number of spangles over a predetermined distance (eg, 100 mm) using a magnified photograph of the surface of the plated steel sheet (eg, three times magnification). The average spangle diameter is calculated from [measurement distance / number of spangles].

When the average spangle diameter is larger than 0.7 mm,
The spangle pattern can be visually identified, and the fine spangle design intended in the present invention cannot be obtained. On the other hand, if the average spangle diameter is 0.7 mm or less, it becomes difficult to visually identify the spangle pattern, and it is possible to obtain a design having a beautiful plated surface made of fine spangles which is the object of the present invention.

According to the method of the present invention, C: 0.02 to 0.08 wt
% Low-carbon Al-killed steel slab or C: 0.006 wt% or less ultra-low-carbon Al-killed steel slab, which is hot-rolled and cold-rolled under specific conditions, and then obtained cold-rolled steel sheet The base material is continuously annealed under specific conditions, and then hot-dip plating is performed in an Al-Zn alloy melting bath having the above composition, so that the average spangle particle size is 0.7 mm or less. A Zn-Al alloy plated steel sheet is manufactured.

The hot-dip plating itself may be performed by a conventional method, and is not particularly limited. Molten Zn containing 40-70% Al
-The bath temperature of the Al alloy plating bath is usually 530 to 600 ° C. The continuously annealed cold-rolled steel sheet is cooled to around the bath temperature and immersed in a hot-dip plating bath while passing through a snout kept in an inert atmosphere so as not to be exposed to the outside air. Immediately after getting out of the bath, the amount of plating is controlled by a conventional coating amount control means such as a gas wiping nozzle. The amount of adhesion is not particularly limited, but is usually 35 to 100 g / m ² per side, preferably
Is 45~90 g / m ^2. The hot-dip plating is usually a double-sided plating, but may be a single-sided plating using a known method.

After controlling the amount of adhesion, the plated steel sheet is cooled to solidify the plating film. The cooling at this time may be ordinary air cooling, and there is no need to perform rapid cooling (eg, extremely increased air flow, water cooling, fine particle spraying, etc.) as employed in the conventional fine spangle technology. Therefore, there is no need to modify the conventional continuous hot-dip plating equipment. Even with ordinary air cooling, the processing, such as hot rolling, cold rolling, and continuous annealing before plating, processing conditions, and the composition of the plating bath are appropriately controlled, preferably the annealing temperature is 650 to 690 ° C, and the plating is performed. A molten Zn-Al alloy plating film having a fine spangle surface with an average spangle diameter of 0.7 mm or less by limiting the bath Si concentration to 0.5 to 2.0 wt% and the remaining Si concentration to 1% or less. Can be.

After cooling, if necessary, the plated steel sheet is lightly reduced with a leveler or a skin pass roll, and then wound up, in order to remove distortion generated during pre-annealing or hot-dip plating. When the spangle is coarse, the spangle becomes non-uniform at the time of the reduction and the appearance is deteriorated, or the appearance becomes uneven after coating. However, in the present invention, since spangles are miniaturized, even when the skin pass pressure is reduced, such deterioration in appearance and unevenness in appearance at the time of painting are hardly observed. Next, the working effects of the present invention will be described more specifically with reference to examples.

[0048]

[Example] Low carbon Al killed steel slab (C: 0.04%)
After hot rolling, cold rolling was performed to obtain a cold-rolled steel sheet having a thickness of 0.8 mm.

After the surface of the cold-rolled steel sheet having a thickness of 0.8 mm was cleaned by alkali degreasing, the steel sheet was subjected to continuous annealing for 60 seconds at an annealing temperature shown in Table 1 in an annealing furnace in an N ₂ + H ₂ gas atmosphere. 2 bath composition shown in: subjecting a double-sided hot-dipping using a (remainder zinc and unavoidable impurities) molten Zn-Al alloy plating bath to control the coating weight of about 70 g / m ² per side at a wiping nozzle, Normal air cooling (air flow 500 Nm ³ / min)
To obtain a hot-dip Zn-Al alloy-plated steel sheet.

The results of the evaluation of the average spangle diameter, workability and corrosion resistance of the obtained hot-dip Zn—Al alloy-plated steel sheet as shown below are shown together with the overall evaluation in Table 2.

Analysis of Alloy Layer After the plating film was dissolved in 10% iodine-ethanol, the remaining alloy layer was dissolved in hydrochloric acid, and the composition was quantified by solution analysis.

Average Spangle Diameter The number of spangles per 100 mm length was measured using a two-fold enlarged photograph of the plating surface, and the average spangle diameter (mm) was calculated from [100 / number of spangles].

FIG. 1 is a graph plotting the residual Si concentration with respect to the average spangle diameter obtained in this manner.

Workability In a 180 ° 2T bending test of a test piece of a plated steel sheet, the crack width and the number of cracks of the plating film at the bent portion were observed with a scanning electron microscope (SEM) and evaluated according to the following criteria. ×: Large crack, partial peeling, Δ: Cracking, no peeling, ○: Small crack, no peeling, ：: Very small crack, no peeling.

Corrosion resistance A salt spray test (JIS Z2371) of a test piece of a plated steel sheet was performed at 2500.
After performing for a time, the area ratio of red rust occurrence is determined by visual judgment,
Evaluation was made according to the following criteria. ×: Red rust generation of 50% or more, Δ: Red rust generation of 5 to 50%, ○: Red rust generation of 5% or less, ：: No red rust at all.

Comprehensive evaluation ×: 2 or more items ×, Δ: 1 item ×, ○: 1 or 2 items are ○, the rest is ◎, ◎: All are ◎. (However, an average spangle diameter of 0.7 mm or less is indicated by ◎, and an average spangle diameter of 0.7 mm or more is indicated by ×).

[0057]

[Table 2]

As can be seen from Table 2, when a hot-dip Zn—Al alloy-plated steel sheet was manufactured according to the present invention, the average spangle diameter was 0.7 mm or less, and the workability and corrosion resistance were good. In contrast, the Al content in the plating bath (plating film) was 40%
When the Si concentration was less than 1% or when the Si concentration of the portion excluding the alloy layer existing at the plating-steel plate interface from the plating film exceeded 1%, the average spangle diameter exceeded 1.0 mm and the spangle became remarkably coarse. The Al content of the plating bath is outside the range of 40-70%,
If the Si content is less than 0.5%, workability and corrosion resistance are significantly deteriorated.

[0059]

According to the present invention, the conventional continuous hot-dip plating equipment can be used as it is without modification, without deteriorating workability and corrosion resistance, and minimizing spangled molten Zn-Al having excellent design properties. It becomes possible to obtain an alloy plated steel sheet.

This plated steel sheet has excellent corrosion resistance typified by a Zn-55% Al alloy plated steel sheet and good workability to withstand severe bending work, and furthermore, from fine spangles which cannot be visually identified. Since it has a highly designable appearance, it can be used for building materials, home appliances, other objects, and the like as it is without painting. In addition, since the spangles are fine, there is little unevenness in appearance after painting, so they can be used for painting applications like automobile bodies, and thus, higher corrosion resistance than conventional galvanized steel sheets on automobile bodies Can be granted.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between Si concentration and spangle diameter in a region excluding an alloy layer in a plating film.

Claims (6)

[Claims] (1) Al: 40 to 70 wt%, Si: 0.5 to 2.0 wt%,
Hot-dip Zn-Al with average plating film composition consisting of residual Zn
In a system alloy plated steel sheet, the Si concentration of the plating film in the region excluding the alloy layer existing at the plating-steel plate interface is 1 wt% or less, lower than the Si concentration of the average plating film composition, and the plating film surface Having an average spangle diameter of 0.7 mm or less
Zn-Al alloy plated steel sheet. 2. The method according to claim 1, wherein the plating film composition further comprises Zr, H
2. The molten Zn according to claim 1, wherein each of at least one selected from the group consisting of f and V contains 0.01 to 0.4 wt%.
-Al-based alloy plated steel sheet. 3. The hot-dip Zn—Al-based alloy-coated steel sheet according to claim 1, wherein the alloy layer has a Si content of 1.5 to 20%, and the deposited amount of the alloy layer is 3 to 6 g / m ^2. . 4. A steel sheet annealed at an annealing temperature of 650 to 690 ° C., immersed in a molten Zn—Al alloy plating bath having a composition of 40 to 70 wt% of Al, 0.5 to 2.0 wt% of Si and the balance of Zn. The plating is characterized by the fact that the Si concentration of the plating film in the region excluding the alloy layer existing at the plating-steel plate interface is 1 wt%.
A method for producing a hot-dip Zn—Al-based alloy-coated steel sheet having a small spangle that is lower than the Si concentration of the plating bath and has an average spangle diameter of 0.7 mm or less on the surface of the plating film. 5. The plating bath further comprises at least one selected from the group consisting of Zr, Hf, and V.
The method for producing a hot-dip Zn-Al-based alloy-plated steel sheet according to claim 4, comprising 0.01 to 0.4 wt%. 6. The hot-dip Zn—Al-based alloy coated steel sheet according to claim 4, wherein the Si content of the alloy layer is 1.5 to 20%, and the adhesion amount of the alloy layer is 3 to 6 g / m ^2. Manufacturing method.