JP2002212699A - HOT DIP Zn-Al ALLOY PLATED STEEL SHEET HAVING EXCELLENT WORKABILITY AND METHOD OF PRODUCING THE SAME - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hot dip Zn-Al alloy plated steel sheet which is free from a honeycomb pattern and has a smooth surface, small spangles and excellent design characteristics, and whose plated film is excellent in workability, and to provide a method of producing the same. SOLUTION: The hot dip Zn-Al alloy plated steel sheet has a plated film which is characterized in that the plated film contains 3.5 to 10% Al, 0.01 to 0.50% Mg, and the balance being Zn and inevitable impurities, the total amount of the inevitable impurities of Pb, Sn, Cd and Bi is <=0.020%, the amount of Fe is <=0.5 g/cm2, the average diameter of the spangles is <=2.0 mm, and the orientation coefficient of Zn (00.2) face parallel to the plated face is <3.5. The steel sheet having such characteristics is produced by plating the steel sheet with a plating bath having a desired chemical composition, rapidly cooling with a cooling speed of 10 to 50 deg.C/s or subjecting the plated steel sheet to a process for spraying a zinc powder onto the plated layer, and subjecting to a post heat treatment comprising keeping at 130 to 350 deg.C for at least 10 s.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-dip Zn-Al-based alloy-plated steel sheet suitable as a material for automobiles, home appliances, building materials and the like, and a method for producing the same. In particular, the present invention relates to a hot-dip Zn-Al-based alloy-plated steel sheet having excellent workability in which a plated film is less likely to crack when processed to a plated steel sheet, and a method for producing the same.

[0002]

2. Description of the Related Art A Zn-Al-based alloy-coated steel sheet containing 3.5 to 6.5% by mass of Al (hereinafter, the unit of chemical composition means% by mass) means that Al is contained. Excellent corrosion resistance compared to hot-dip galvanized steel sheet. In addition, Zn-
Since the plating bath of the Al-based alloy has a chemical composition close to the eutectic point, it has a lower melting point than Zn and can be hot-dipped at a lower temperature than hot-dip galvanizing. This can suppress the development of the alloy layer at the plating film interface,
By the plating, a plated steel sheet having good workability such as bending of a plating film can be obtained. For this reason, the Zn-Al-based alloy-plated steel sheets are used for building materials such as roofs and walls, civil engineering products such as guardrails, wiring pipes and soundproof walls, heat shield plates for automobiles, and home appliances such as electric washing machines and microwave ovens. It is rapidly spreading as a material for products and the like.

When hot-dip plating in a plating bath having a chemical composition near the eutectic point, the resulting plating film may have a turtle pattern. The turtle pattern is a kind of surface defect in which a linear concave portion having a small amount of plating adhesion is continuously formed in a turtle shape on the plating film surface. The turtle pattern is the final solidified portion where the molten plating layer solidifies. Since the depth of the concave portion is large, it is visually recognized as a poor appearance even after painting. For this reason, it is not preferable for a painted product that emphasizes appearance.

As described in Japanese Patent Application Laid-Open No. 02-175852, it is known that a turtle pattern can be prevented by adding Mg to a Zn-Al alloy plating bath. However, when Mg is contained in the plating film, there is a problem that the hardness of the plating film increases, the ductility is impaired, and the workability of the plating film is significantly reduced.

[0005] In recent years, in addition to corrosion resistance, the design of plated steel sheets has also been emphasized, and there has been a demand for plated steel sheets which are excellent in design without spangles and glare due to metallic luster. Have been. For this reason, a plated steel sheet (minimum spangle) with a reduced spangle and a method of manufacturing the same have been proposed.

[0006] For example, Japanese Patent Application Laid-Open No. 10-88310 discloses that a plating layer having a temperature equal to or higher than a solidification start temperature is sprayed with water or a mixture of water and a chemical solution to rapidly solidify the plating layer (hereinafter, referred to as a "solid").
This cooling method is also referred to as "water-water cooling"), and a Zn-Al-based alloy-plated steel sheet having an antiglare property has been proposed in which the spangle of the plating film is reduced and the gloss thereof is 100 or less.

Japanese Patent Application Laid-Open No. Hei 10-265931 has a Zn-Al alloy plating film containing 3.1 to 5.5% of Al, and sprays water or a chemical solution when the plating layer is in a molten state. As a result, the surface roughness of the plating film is reduced to R
a is set to 1.5 μm or more, and the static friction coefficient μ is set to 0.23 or more to make the plating layer less slippery.
l-based alloy plated steel sheets have been proposed.

[0008]

However, if the plating bath is made to contain Mg to prevent a turtle pattern as proposed in Japanese Patent Application Laid-Open No. 02-175852, the resulting plating film is hard. , And the ductility is reduced, and the workability of the plating film is significantly impaired. Also, JP-A-10-88310 and JP-A-10-26
As proposed in Japanese Patent No. 5931, the workability of the plating film is also impaired by rapidly cooling the hot-dip coating layer in order to improve the design of the plating film. In particular, when the hot-dip coating layer contains Mg, if the hot-dip coating layer is rapidly cooled and solidified by air-water cooling to form a minimum spangle, the rapid solidification and the Mg content cause a synergistic effect. The processability of the coating is further reduced.

For this reason, in a plated steel sheet which is free of a crack pattern and which has an excellent design of a minimum spangle pattern, for example, a crack is formed in a plated film in a portion subjected to severe bending, and corrosion proceeds from that portion. Therefore, there is a problem that the corrosion resistance of the processed portion is impaired, and the commercial value of the processed product is quickly lost despite the good corrosion resistance of the flat plate portion.

As a method of obtaining a minimum spangle, there is a method of performing temper rolling after hot-dip plating. However, in this method, the properties of the base material may be deteriorated, and the plated film may be damaged by the temper rolling and the plated film may be damaged. This is not a sufficient method because workability may be impaired.

Japanese Patent Application Laid-Open No. 4-41657 discloses a plating method for improving the workability of a plating film by subjecting a plating surface of a Zn—Al-based alloy-coated steel sheet to a blast treatment and then performing a low-temperature short-time heat treatment. Although proposed, this method requires new capital investment, although inline processing is possible. Furthermore, it is unsuitable for applications that emphasize surface quality.

As described above, in a hot-water-cooled hot-dip Zn-Al-based alloy plated steel sheet containing Mg for smoothing the plating film and adjusting the spangle, the workability of the plating film obtained is as follows: Not always enough. For this reason, corrosion resistance may be unfavorable in a part that has been subjected to severe processing, and a solution to this problem has been strongly demanded.

The object of the present invention is to solve these problems,
Molten Zn- with smooth surface, no spangles, small spangles, excellent design, and excellent workability of plating film
An object of the present invention is to provide an Al-based alloy-plated steel sheet and a method for producing the same.

[0014]

Means for Solving the Problems In order to improve the corrosion resistance of a Zn-Al based alloy plating film containing Mg after processing, it is important to improve the workability of the plating film itself. As a result of repeated research on the conditions, the following new findings were obtained.

A. In order to contain Mg to prevent a turtle pattern and to form a minimum spangle, the molten Z
n The Zn-Al-based alloy plating film produced by rapid cooling by applying air-water cooling after plating, the frequency of cracking of the plating film during processing and the number of The size (crack width) increases. The cracking position is often the lamellar eutectic part or the boundary between the eutectic part and the Zn phase.

In the case of the conventional Zn-Al alloy plating containing no Mg, the eutectic portion is easily deformed during bending to suppress the generation of cracks. It was presumed that in the plating film containing Mg, the ductility of the eutectic portion was remarkably reduced, so that cracks were easily generated during processing.

B. If the cooling rate at the time of solidification of the hot-dip coating layer is increased, or so-called Hearty treatment for spraying Zn powder on the hot-dip coating layer to promote nucleation of spangles, the spangles of the resulting plating film are reduced and Zn The (00 · 2) plane of the crystal structure (hereinafter referred to as “Zn (00
・ 2) plane ”is preferentially oriented parallel to the plating film surface, and the Zn (00 · 2) plane has a high orientation.

A plating film having a high orientation of the Zn (00 · 2) plane is less likely to cause twin sliding deformation inside the plating film, and thus such plating film has poor workability. This means that by reducing the orientation of the Zn (00 ・ 2) plane of the plating film, twin sliding deformation during processing is promoted, and the deformability of the plating film is increased to improve the workability of the plating film. Can be improved.

C. By subjecting the plating film, which has been subjected to air-water cooling and the like to a small spangle when the plating layer is solidified, to a small spangle, it is subjected to a process of holding it for a short time at a moderately high temperature range (hereinafter simply referred to as "post-heat treatment"). The orientation of the plating film to be obtained can be easily randomized.

That is, by performing the post heat treatment at a temperature equal to or higher than the recrystallization temperature of Zn, recrystallization is caused and the orientation of the plating film can be randomized. Further, by performing post-heat treatment, Al and Mg which are dissolved in Zn in a supersaturated manner by Zn from rapid melting from a high temperature molten state are precipitated, the supersaturated state is eliminated, and the internal strain existing in the plating film is relaxed. Also,
It is presumed that it contributes to the improvement of the workability of the plating film.

The present invention has been completed on the basis of these findings, and the gist of the invention is as follows: (1) a hot-dip Zn-Al-based alloy-plated steel sheet having excellent workability;
(3) The manufacturing method described in (3).

(1) At least one surface of the base material is molten Zn-A
A steel sheet provided with an l-based alloy plating film, wherein the plating film has a chemical composition of 3.5%
% Or less and Mg of 0.01% or more and 0.50% or less, and the balance consists of Zn and unavoidable impurities. The total content of Pb, Sn, Cd and Bi as unavoidable impurities is 0.020. % Or less, F contained in the plating film
e The content is 0.5 g / m ² or less, the average diameter of spangles is 2.0 mm or less, and the orientation index of Zn (00 · 2) plane parallel to the plating surface is less than 3.5. Hot-dip Zn-Al alloy coated steel sheet with excellent workability.

(2) The base material contains 3.5% or more and 10% or less by mass of Al, 0.01% or more and 0.50% or less of Mg, and the balance consists of Zn and unavoidable impurities. ,
After being immersed in a hot-dip plating bath having a total content of Pb, Sn, Cd and Bi as unavoidable impurities of 0.020% or less, pulled up to adjust the plating adhesion amount, and then subjected to steam-water cooling, A molten Zn-Al system excellent in workability, characterized by cooling at a rate of 50 ° C./second or cooling by applying a hearty treatment and then performing a heat treatment after holding at a temperature range of 130 to 350 ° C. for 10 seconds or more. Manufacturing method of alloy plated steel sheet.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail. Chemical composition of plating film: Al: The content of alloying elements such as Al and Mg in the plating film is almost the same as the content in the plating bath. Zn-A
In the l-based plating film, Al has an effect of improving the corrosion resistance of the plating film. To ensure this effect, Al
Of 3.5% or more. Desirably, it is 4.0% or more.

If Al is contained in excess of 10%, the melting point of the plating bath rises, the Fe-Al alloy layer develops, and the workability of the plating film is impaired. For example, cracks easily occur in the plating film even in bending and the like, and problems such as deterioration in corrosion resistance of the bent portion occur. There is a method of adding Si or the like to suppress the development of the alloy layer, but this method has a problem that the management of the plating bath becomes complicated. To avoid these disadvantages, the Al content is set to 10% or less. Desirably, it is 7% or less.

Mg: Mg has the effect of spheroidizing the Al-rich phase of the Zn-Al eutectic structure of the plating layer and increasing the volume fraction of the β-Zn phase. The effect that generation is reduced is obtained. To obtain this effect, Mg is contained in an amount of 0.01% or more. Desirably, it is 0.05% or more. On the other hand, if Mg is excessively contained, the plating film becomes hard and workability is impaired. If the Mg content exceeds 0.50%, the workability improvement effect will not be sufficient even if the orientation of the plating film described later is controlled to be low, so the Mg content is set to 0.50% or less. Desirably, it is 0.30% or less.

Pb, Sn, Cd and Bi: When these elements are contained in the plating bath, they are segregated at crystal grain boundaries when subjected to rapid cooling such as steam-water cooling during cooling after plating. Intergranular corrosion progresses when used as a plated steel sheet,
In some cases, the peeling resistance of the plating film over time is impaired. To prevent this, the content of these four elements is set to 0.020% or less in total. Desirably, it is 0.010% or less. Note that the reduction of these elements may be performed by preventing mixing from the dissolving material when adjusting the plating bath.

Fe: The Fe content of the plating film is as follows:
Increases with the growth of the alloy layer formed at the plating interface,
The alloy layer easily grows when the plating bath temperature, the immersion temperature of the base material in the plating bath, and the like are increased. When the Fe content increases beyond 0.5 g / m ² per area of the plated surface, the workability is significantly reduced.
g / m ² or less. Desirably, it is 0.2 g / m ² or less.

The balance is Zn and unavoidable impurities.
Note that Ni, Cr, Mo, W, Si are inevitable impurities.
, B, Be and the like are contained in the plating film in the range of 0.02% or less, respectively, without impairing the effects of the present invention. Therefore, even if these elements are contained in the above range, there is no problem in obtaining the desired effect of the present invention.

Spangle diameter: When the average diameter of the spangle exceeds 2.0 mm, the luster between adjacent spangles differs, and depending on the viewing angle, the color tone is greatly different between the steel plates and is visually recognized. May be impaired. To prevent this, the spangle diameter (size)
The average diameter is limited to 2.0 mm or less. When more emphasis is placed on the design, it is desirable to be 1.5 mm or less. This average diameter can be easily measured by observation with an optical microscope.

[0031] Orientation index of Zn (00 · 2) plane: By reducing the orientation of Zn (00 · 2) plane, twin sliding deformation easily occurs in the plating film, and the workability of the plating film is improved. Can be improved.

When the Zn plating skin layer in the molten state is cooled, Zn (00 ·
2) The degree of surface integration increases. This phenomenon is the same even when the plating bath contains Al or when a so-called Hearty treatment or the like for spraying Zn powder on the hot-dip coating layer is performed.

When the orientation index of the Zn (00 · 2) plane is 3.5 or more, the deformability of the Zn phase dispersed in the plating film is poor, the crack in the bent portion becomes large, and the corrosion resistance of the bent portion becomes poor. It decreases significantly. For this reason, the plated steel sheet of the present invention has an index (orientation index: _Ia ) representing the strength of the orientation of the Zn (00 · 2) plane of less than 3.5. Desirably, it is 2.5 or less.

The orientation index (I _a ) is calculated by the following method. The X-ray diffraction intensity of the (hk · l) plane of the plating film surface was measured using a Co bulb under the conditions of an acceleration voltage of 30 kv and a current of 100 mA, and the value calculated from the result by the following equation was defined as Ia.

[0035] [Equation 1] where, I _(hk · _l): integrated intensity of the X-ray diffraction (hk · l) _{plane, I F (hk · l)} : in the X-ray diffraction (hk · l) surface of Integral intensity ratio, I _{FR (hk} · _l) : intensity ratio in X-ray diffraction of (hk · l) plane described in ASTM card.

Other than the above, it is optional. A hot-dip coated steel sheet satisfying the above conditions may be used as it is, or a rust-preventive oil, a lubricating rust-preventive oil, a chromate Known post-treatments such as a coating, a resin coating, and a chromate / resin composite coating may be applied to the plating film.

Manufacturing method of steel sheet of the present invention: An example of a preferable manufacturing method of a hot-dip Zn-Al-based alloy-plated steel sheet of the present invention having excellent workability is shown below. However, the method described below is an example, and the method for producing a plated steel sheet according to the present invention is not limited thereto.

As the base material, either a hot rolled plate or a cold rolled plate may be used. When using a cold rolled sheet as the base material,
It is economical and desirable to use one that has not been annealed,
Annealed ones may be used.

A known plating method may be used. First,
The pretreatment is performed so that the surface of the base material is suitable for hot-dip plating. As the pretreatment method, a known method such as washing with an aqueous alkali solution or grinding the surface with a nylon brush or the like can be applied.

Subsequently, the base material was heated at 600 ° C. in a reducing atmosphere.
After heating for the above-mentioned or above the recrystallization temperature and holding for a required time, it is cooled to near the plating bath temperature and immersed in a hot-dip plating bath. The heating atmosphere of the base material is, for example, 5-30 hydrogen.
The reducing atmosphere may be a commonly used reducing atmosphere, such as a volume% content, the balance being nitrogen, and a dew point of −60 ° C. or more and −10 ° C. or less.

The content of alloying elements such as Al and Mg in the plating film is almost the same as the content in the plating bath. Therefore, the chemical composition of the plating bath may be the same as the desired alloy composition. The temperature of the plating bath is preferably higher by 30 to 60 ° C. than the melting point of the alloy of the plating film composition. 60 ° C
If it is higher than, the development of the alloy layer when immersed in the plating bath becomes remarkable, which is not preferable.

The base material is immersed in a plating bath, and the amount of plating applied is adjusted to a predetermined amount by a known method such as a gas drawing method. The adhesion amount of the plating film is not particularly specified in the present invention, but is required to be 4 per side in order to secure appropriate operation efficiency.
A range from 0 to 250 g / m ² is preferred.

Next, water droplets, or water droplets and high-pressure air,
Further, a mist obtained by mixing ammonium phosphate or the like with these is subjected to steam-water cooling to spray the hot-dip coating layer to rapidly cool the coating layer at a cooling rate of 10 ° C./second or more.
Cooling is performed by applying a so-called Hearty process of spraying Zn powder. This makes it possible to reduce the spangle diameter and provide a plated steel sheet having excellent design properties that does not vary between steel sheets.

In the air-water cooling, when the cooling rate exceeds 50 ° C./sec, the effect of reducing the spangle diameter is saturated.
The cooling rate is preferably 50 ° C./second or less. After adjusting the amount of adhesion, the above-mentioned rapid cooling is preferably performed at least until solidification of the plating layer is completed.

After the plating film solidifies, the temperature is 130 ° C. or more.
A post-heat treatment is performed in a temperature region of 350 ° C. or less to stay for 10 seconds or more. If the post heat treatment temperature is lower than 130 ° C, Z
It is difficult to make the orientation of the n (00 · 2) plane less than 3.5. In order to efficiently reduce the Zn (00 · 2) plane orientation, it is desirable to set the post heat treatment temperature to 150 ° C. or higher.

When the post heat treatment temperature exceeds 350 ° C., Zn
Al and Mg again form a solid solution and the plating film becomes hard, which is not good. Further, when the material is heated to a high temperature region (for example, 400 ° C.) where Zn is re-melted, spangles are sublimated and the design property is deteriorated. Preferably it is 300 ° C. or lower.

If the staying time in the above temperature range is less than 10 seconds, the orientation index is not sufficiently reduced, and the workability of the film is not improved. For this reason, the staying time in the above temperature range is set to 10 seconds or more. The staying time does not necessarily need to be maintained at a uniform temperature, but may be at least 10 seconds in the temperature range. More preferably, it is 20 seconds or more. If the holding time is excessively long, the effect of reducing the Zn (00 · 2) plane orientation is saturated and the productivity may be impaired. Therefore, the holding time is preferably 180 seconds or less at the longest.

The timing of the post-heat treatment may be during the cooling after the hot-dip plating and the adjustment of the adhesion amount, or may be performed after adjusting the adhesion amount and once cooling to 130 ° C. or lower, and then heating to the post-heat treatment temperature region. You may give it.

The above hot-dip coated steel sheet is coated with a rust-preventive oil, a lubricating rust-preventive oil, a chromate, a resin coating, a chromate / resin coating, etc.
Is applied according to a known method.

[0050]

EXAMPLE An unannealed low-carbon cold-rolled steel sheet containing 0.05% of C and 0.28% of Mn and having a balance of substantially Fe and a thickness of 0.70 mm was used as a plating base material. 75 of this base material
Degreased with NaOH solution at ℃, washed and heated to 800 ℃ in an atmosphere containing 20% by volume of hydrogen, the balance consisting of nitrogen and dew point of -40 ℃, holding for 60 seconds to recrystallize After annealing, it was cooled to near the plating bath temperature and immersed in a hot-dip plating bath.

The chemical composition of the plating bath is as follows: Al: 3.0 to 1
2%, Mg: 0 to 0.8%, the balance being Zn containing Fe to saturation, and the temperature was set to the melting point + 40 ° C. After the base material was immersed in a hot-dip plating bath and pulled up, the coating weight was adjusted to 150 g / m ² (per one side) by a gas drawing method. After plating, the film was cooled slowly or by air-water cooling in which the amount of water contained was variously changed, and the spangle diameter of the resulting plating film was adjusted to various sizes.

Various properties of the obtained plated steel sheet were evaluated by the following methods. Average diameter of spangle: Twenty spangles were randomly extracted, the average value of the maximum diameter and the minimum diameter was measured, and the average of the 20 measured values was defined as the average diameter of the plated steel sheet.

Orientation index of Zn (00 · 2) plane: As a sample for X-ray diffraction, six 25 mm square sample pieces were sampled from an adjacent portion of a plated steel sheet, and a Co tube was sampled using a commercially available electron microscope. The X-ray diffraction integrated intensities of these specimens were measured using a sphere under the conditions of an acceleration voltage of 30 kv and a current of 100 mA, and the average value of six specimens was taken as a representative value Ia of the plated steel sheet.

Bending workability of plating film: The test piece was subjected to 180 ° bending processing with an inner bending diameter of 0.7 mm (equivalent to the plate thickness), and the occurrence of cracks in the plating film outside the bent portion was measured using an optical microscope. Observation was made and the bending workability was evaluated according to the following four grades according to the state of occurrence of cracks. A: No crack is observed. ：: Small cracks are partially observed. Δ: Small cracks are observed on the entire surface. X: Large and small cracks are mixed and observed on the entire surface.

Corrosion resistance of the flat part and the processed part: 150 m long
m, a test piece for a flat plate part whose end face is sealed with a tape having a width of 70 mm, and an inner bending diameter of 1.4 mm for the test piece.
Was prepared and subjected to the following cyclic corrosion test to determine the number of days until red rust occurs on the flat plate portion or the bent portion.
The corrosion cycle was one cycle (one day) of salt spray (35 ° C. × 6 hours) → drying (60 ° C. × 12 hours) → wetting (50 ° C. × 6 hours). The corrosion resistance is 2 for the flat part.
The case where red rust did not occur for 5 days or more and for the processed portion for 10 days or more was evaluated as good.

Temporal peeling resistance: length 100 mm, width 25
24 mm at 80 ° C and 95% relative humidity.
After a corrosion test of holding for 0 hours, a bending process with an inner bending diameter of 1.4 mm is performed, an adhesive tape is applied to the bent portion and peeled off, and a visual observation of the peeling state of the plating film by the adhesive tape is performed. The results were evaluated according to the following criteria. ：: No peeling was observed at all. ○: Slight peeling was observed at the edge, but passed. ×: Linear peeling was observed in the width direction of the bent portion and rejected. Design: 70 mm in size from each plated steel sheet. Five test pieces of × 70 mm were sampled, and the gloss of the plating surface of these test pieces was measured using a commercially available gloss meter according to the 20-degree specular gloss measurement method described in JIS-Z8741.
The specular gloss was measured. The average value of the measured values of the five samples was 20 or more and 40 or less, good (○), the case of more than 40 and 60 or less was bad (△), and the case of more than 60 was extremely bad. (X), the designability was evaluated.

Table 1 shows the cooling conditions after plating, the chemical composition of the plating film of the resulting plated steel sheet, the orientation index of the Zn (00 · 2) plane, the performance evaluation results of the plating film, and the like.

[0058]

[Table 1] As shown in Table 1, the plated steel sheet satisfying the conditions specified by the present invention had good bending workability of the plating film, a small spangle diameter, excellent design, good corrosion resistance, and good anti-peeling property over time. . Those having a total content of (Pb + Sn + Bi + Cd) of 0.090% or less had particularly good peeling properties over time. In Test No. 24 where the post-heat treatment was sufficiently performed, the orientation index of the Zn (00 · 2) plane was particularly low, and the corrosion resistance of the processed portion was excellent.

On the other hand, in Test No. 1 in which the Al content of the plating film was small, the corrosion resistance of the flat plate portion was not good. Test No. 6 with too high Al content, Test No. 11 with too high Mg content, Test No. 1 with too high Fe content
6. In Test Nos. 19 and 20, in which the post-heat treatment conditions were unfavorable and Ia was high, the bending workability of the plating film was not good. In Test Nos. 15 and 26 in which the total content of (Pb + Sn + Bi + Cd) was large, the peeling resistance with time was not good. Test No. 7 in which Mg content was too low, Test No. 1 in which cooling conditions after plating were not favorable conditions
7, 18, 26, Test No. 25 in which spangles sublimated due to too high post-heating temperature, the spangles were too large and the design was poor. Test numbers 15 and 26
The reason why the spangle was large was that the content of Pb and the like was too high.

[0060]

The hot-dip Zn—Al-based alloy-coated steel sheet of the present invention has a flat surface because it has no crack pattern, has a smooth surface, has small spangles, and has excellent design properties, and has excellent workability of the plating film. In addition, it has excellent corrosion resistance in the processed part. Therefore, it is useful as a building material product such as a roof or wall material, a guard rail, a wiring pipe, or a soundproof wall. Further, since this steel sheet can be manufactured efficiently without using special equipment, it is excellent in economical efficiency.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Ken Tomiya 4-5-33 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture F-term in Sumitomo Metal Industries, Ltd. (reference) 4K027 AA02 AA22 AB44 AC62 AC64 AC66 AE03 AE12 AE18 AE21 AE25

Claims (2)

[Claims] 1. A steel sheet provided with a molten Zn—Al-based alloy plating film on at least one surface of a base material, wherein the plating film has a chemical composition of 3.5% or more and 10% or less of Al in mass%. Mg of 0.01% or more and 0.50% or less, the balance consisting of Zn and unavoidable impurities, and the total content of Pb, Sn, Cd and Bi as unavoidable impurities is 0.020% or less; Fe content contained in the plating film 0.5 g / m ² or less, 2.0 mm average diameter spangle
A hot-dip Zn-Al-based alloy plated steel sheet excellent in workability, characterized in that an orientation index of a Zn (00 · 2) plane parallel to a plating surface is less than 3.5. 2. The base material has a content of at least 3.5% by mass of Al,
It contains not more than 10% and not more than 0.01% and not more than 0.50% of Mg, and the balance consists of Zn and unavoidable impurities, and the total content of Pb, Sn, Cd and Bi as unavoidable impurities is 0.1%. Immersed in a hot-dip plating bath of 020% or less and pulled up to adjust the amount of plating applied, and then cooled by air-water cooling at a cooling rate of 10 to 50 ° C./sec, or cooled by applying a hearty treatment, A method for producing a hot-dip Zn-Al-based alloy-plated steel sheet having excellent workability, which is followed by performing a post-heating treatment at a temperature of 130 to 350 ° C. for 10 seconds or more.