JP2007107050A - HOT DIP Al BASED PLATED STEEL SHEET HAVING EXCELLENT WORKABILITY AND METHOD FOR PRODUCING THE SAME - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the workability and corrosion resistance after working in an Al plated steel sheet by reducing the thickness of an alloy layer upon the production of the Al plated steel sheet. <P>SOLUTION: In the method for producing a hot dip Al plated steel sheet having excellent workability, when a steel sheet is subjected to continuous hot dip Al plating, the content (mass%) of Si in an Al plating bath and bath temperature (°C) are allowed to satisfy the inside of a quadrilateral ABCD shown by the following, and the bath temperature is defined as T°C, the content of Fe in the Al plating bath is controlled to 0.03T-17.6 mass% or above: A (4.2%, 635°C), B (7%, 635°C), C (10%, 680°C), D (6.5%, 680°C). According to this invention, the reduction of unplating is simultaneously made possible. Further, the production of the hot dip Al plated steel sheet having extremely excellent characteristics overall is made possible. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a molten Al-based plated steel sheet having excellent corrosion resistance and heat resistance used for metal building materials such as roof walls, household and industrial electrical appliances, automobile exhaust system members, fuel tank materials, and the like, and a method for producing the same. About.

  In general, a hot-dip Al-plated steel sheet is widely used in automobile parts, building materials, home appliance parts, and the like because of its high corrosion resistance, heat resistance, beautiful appearance, and the like. In the old days, an oxidation furnace method was used as a continuous hot dipping process for continuously plating steel strips. In this method, the surface of the steel sheet is weakly oxidized in an oxidation furnace and then reduced in a subsequent reduction furnace to increase the reactivity with the Al plating bath on the surface. However, in this method, the reaction time in the reduction furnace is required, so the line speed cannot be increased. For this reason, a method called a non-oxidizing furnace method that oxidizes extremely weakly in a combustion atmosphere was adopted. This makes it possible to improve the line speed (productivity) and has become a general manufacturing method.

  In this non-oxidizing furnace method, there is a concern that the scale when weakly oxidized in the non-oxidizing furnace is picked up by a roll or the like in the furnace and scratches the steel sheet, and alloyed Zn-plated steel sheet that requires a strict appearance quality, etc. Instead of this, the RTF (Radiant Tube Furnace) method has come to be used instead. This is equipped with a degreasing equipment in front of the line and heats the degreased steel sheet in a reduction furnace, and this method makes it possible to eliminate scale-induced wrinkles. Since this method tends to increase the size of the equipment and increases the initial equipment cost, it is applied to applications that require appearance quality. The maximum use of the hot-dip Al-plated steel sheet is an automobile exhaust system member, and since the quality required for appearance in this application is not so high, it is often manufactured by a non-oxidation furnace method.

  By the way, generally, hot-dip Al plating tends to cause a defect in which a minute uncoated portion called non-plating is likely to occur as compared with hot-dip Zn plating. This is because the surface energy of the molten Al itself is relatively high, and Al has a very high affinity with gas components such as oxygen, nitrogen, hydrogen, etc., and a compound with these gas components is formed on the surface of the molten Al to form a steel sheet. The reason is that it is easy to be caught when immersed in molten Al. For this reason, various improvements have been made to eliminate non-plating. For example, Japanese Patent Laid-Open No. 61-190056 (Patent Document 1) discloses a technique for controlling the atmosphere of a penetration portion of a steel plate called snout into a plating bath.

  In recent years, the need for Al plating on Cr-containing steels and stainless steels has increased, and as a technology for suppressing non-plating even when these original plates that are more prone to surface defects such as non-plating are used, Fe, Ni, etc. JP-A-1-28341 (Patent Document 2) as a technology for pre-plating, and JP-A-7-286252 (Patent Document 3) as a technology for increasing the hydrogen concentration in the annealing furnace, operating conditions of CGL JP-A-5-31380 (Patent Document 4) has been developed as a technique for optimizing the above.

  In addition, as a major problem with hot-dip Al-plated steel sheets, the intermetallic compound layer (hereinafter referred to as alloy layer) generated at the interface between the Al-plated layer and the steel sheet is thicker than Zn-plated steel sheets, and cannot withstand severe processing. A point is mentioned. Since this alloy layer is generally extremely hard and brittle, there is a problem that when it is processed, it becomes a starting point of fracture, and cracks of the Al plating layer are caused from this starting point. Further, when the alloy layer is severely broken, the adhesion at the interface is lost and the Al plating layer is peeled off. When complicated molding is required, such as automobile fuel tank material, it is molded by applying a lubricating film to the surface as disclosed in Japanese Patent Laid-Open No. 2001-19902 (Patent Document 5). Further, even cracks generated in the Al plating layer cannot be completely suppressed, and improvement from the Al plating side is demanded.

Japanese Patent Laid-Open No. 61-190056 Japanese Patent Laid-Open No. 1-28341 JP 7-286252 A JP-A-5-31380 Japanese Patent Laid-Open No. 2001-19902 JP 2000-239819 A

  In view of the above, the present invention discloses a technique for reducing the thickness of an alloy layer when manufacturing an Al-plated steel sheet. Moreover, it is possible to suppress the occurrence of non-plating as a secondary action at this time, and it is possible to manufacture a hot-dip Al-plated steel sheet having extremely excellent characteristics overall.

The present inventors obtained the following knowledge by adding thermodynamic examination to many experimental facts.
That is, since an alloy layer is very easy to grow in the hot Al plating process, Si is usually added to the bath. It is said that the alloy layer produced thereby changes from the Al—Fe system to the Al—Fe—Si system and its growth rate decreases. The amount of Si added is usually about 10%. However, the present inventors have clarified the optimum amount of Si from the analysis of the phase diagram of the Al—Fe—Si system. Similarly, Japanese Patent Application Laid-Open No. 2000-239819 (Patent Document 6) also presents appropriate conditions from the Al—Fe—Si phase diagram, but it is disclosed that the conditions for equilibration with the θ phase are optimal. It is noted that the contents are completely different from the present invention.

FIG. 1 shows an Al—Fe—Si ternary phase diagram (calculated by Thermo-calc) at 650 ° C. In the Al—Fe binary reaction not containing Si, three types of Fe—Al intermetallic compounds of θ (FeAl ₃ ), Fe ₂ Al ₅ , and FeAl ₂ can be generated. It shows that there can be two types of intermetallic compounds, α and β, when Si is added to the Al bath. The α phase is a phase sometimes denoted as τ5 or [AlFeSi] H, and its crystal structure is hexagonal.

As can be seen from FIG. 1, the composition is composed of about 60% Fe, about 9% Si, and the balance Al. The β phase is also described as τ6 or [AlFeSi] M phase and has a monoclinic structure. Its composition is about 60% Fe, about 15% Si, and the balance Al. The clear chemical formula of these compounds is not clear. The θ phase is a phase having a chemical formula of FeAl ₃ and does not contain Si.

  When Al-10% Si reacts with a steel plate (Fe), the reaction is represented by a line connecting Al-10% Si and Fe in FIG. However, the line connecting Al-10% Si and Fe passes near the boundaries of α + L and β + L, and it is not clear which of α and β is produced as an Al plating alloy layer in this state. It can be seen from this figure that the β phase is likely to be generated when the Si concentration is high, and the α phase is likely to be generated when the Si concentration is low. As a result, the plating wettability was improved and the growth of the alloy layer was suppressed. The reason for this is unclear because the chemical formula and physical properties of the α phase and β phase are not clear, but it is known that the void concentration in the intermetallic compound is high in this system. It is presumed that the diffusion behavior differs due to the difference in the pore concentration between the β and β phases. Further, the α phase is considered to have improved wettability because it is more stable in terms of free energy of formation.

  Furthermore, by calculating such a phase diagram while changing the temperature, it was confirmed that the stability of the α phase and the β phase depends not only on the amount of Si in the bath but also on the temperature. FIG. 2 shows a state diagram obtained by calculating how the alloy layer generated when the temperature and the amount of Si are changed is calculated. This figure shows the region where the α phase becomes the alloy layer. However, in practice, it is difficult to operate in the entire region where the α phase becomes an alloy layer. That is, if the bath temperature is too low, the viscosity of the bath becomes high and it becomes difficult to control the amount of plating. On the other hand, if the bath temperature is too high, the equipment in the bath is severely melted, requiring frequent replacement. The present invention has been completed in consideration of such conditions.

The present invention completed based on such knowledge is as follows.
(1) When continuous hot-dip Al plating is performed on a steel sheet, the amount of Si in the Al plating bath (% by mass) and the bath temperature (° C) are set inside the quadrilateral ABCD shown below, and the bath temperature is set to T ° C. A method for producing a hot-dip Al-plated steel sheet excellent in workability, characterized in that the amount of Fe in the Al plating bath is 0.03T-17.6% by mass or more.
A (4.2%, 635 ° C), B (7%, 635 ° C), C (10%, 680 ° C), D (6.5%, 680 ° C)

(2) When continuous hot-dip Al plating is performed on a steel sheet, the amount of Si in the Al plating bath (mass%) and the bath temperature (° C) are set inside the pentagonal ABCDE shown below, and the bath temperature is set to T ° C. Sometimes, the amount of Fe in the Al plating bath is 0.03T-17.6% by mass or more, and the method for producing a hot-dip Al plated steel sheet excellent in workability.
A (4.2%, 635 ° C), B (7%, 635 ° C), C (9%, 664 ° C), D (9%, 680 ° C), E (6.5%, 680 ° C)

(3) The processing according to (1) or (2) above, wherein the temperature of the penetration of the steel sheet into the bath during continuous molten Al plating on the steel sheet is T-25 ° C or higher and T + 25 ° C or lower. A method for producing a hot-dip Al-plated steel sheet having excellent properties.
(4) Any one of (1) to (3) above, wherein the amount of iron powder adhering to the annealing furnace before continuous molten Al plating is 0.5 g / m ² or less per side. The manufacturing method of the hot-dip Al-plated steel plate excellent in the workability as described in 2.
(5) Processing characterized in that the Si amount in the intermetallic compound layer present at the interface between the steel plate and the Al plating layer is 5 to 12% by mass and the average thickness is 2.5 μm or less. It is in hot-dip Al-plated steel sheet with excellent properties.

  The present invention provides a hot-dip Al-based plated steel sheet with few plating defects and a reduced thickness of the alloy layer and a method for producing the same.

Next, the reasons for limiting the present invention will be described in detail.
First, as the composition of the Al-based plating bath, Si is added based on Al as described above, but the amount of Si in the bath is A (4.2%, 635 ° C.), B in relation to the bath temperature. (7%, 635 ° C.), C (9.5%, 670 ° C.), and D (6.2%, 670 ° C.). These conditions correspond to the conditions in which the upper and lower limits of the bath temperature are set slightly inside the α phase region shown in FIG.

  FIG. 2 shows the stable region of the α phase obtained from the phase diagram. However, when actually experimented, the stable region of the α phase tended to be slightly narrowed particularly at higher Si. This is because the phase diagram deals with an equilibrium state, whereas hot dipping deals with a system that reacts at a high speed, and this shift is considered to have occurred. For these reasons, A (4.2%, 635 ° C), B (7%, 635 ° C), C (9%, 664 ° C), D (9%, 680 ° C), E (6.5%, The α-phase alloy layer can be obtained more stably in the pentagon at 680 ° C. The reason why the upper and lower limits of the bath temperature are determined is to avoid operational problems such as an increase in bath viscosity and erosion of equipment in the bath as described above.

  In the present invention, it is desirable that the intrusion plate temperature is a bath temperature of −25 ° C. or higher and a bath temperature of + 25 ° C. or lower. FIG. 2 shows the relationship between the amount of Si and the temperature. The temperature mainly corresponds to the bath temperature in hot dipping, but the temperature when the steel sheet is immersed in the bath is also an important factor. If the intrusion plate temperature at this time is too high, it corresponds to the state in which the temperature in FIG. 2 is high, and the θ phase is easily generated. On the other hand, if the intruding plate temperature is too low, a surface defect called dross tends to occur due to the difference between the bath temperature and the plate temperature. Dross is an intermetallic compound crystallized from molten metal floating in the bath and adhering to the surface of the steel sheet, and the alloy layer and the components are the same. If the intruding plate temperature is significantly lower than the bath temperature, the molten metal is cooled in the vicinity of the steel plate and this dross is generated.

  Next, the amount of Fe in the bath will be described. Usually, in the Al plating bath, Fe melted from the steel plate or the equipment in the bath is dissolved. If the bath temperature is determined thermodynamically, a certain value of the saturation concentration of Fe is determined, but the actual Fe concentration is not a thermodynamic saturation concentration, and is slightly lower than the saturation concentration. The reason for this is still unclear, but it is considered that it is affected by the saturation concentration at a low temperature due to the influence of the temperature distribution in the plating bath. At this time, it was found that the alloy layer easily grows when the Fe concentration in the bath is low. Therefore, it is desirable to increase the Fe concentration in the bath, and this can be achieved by reducing the temperature distribution in the bath. Specifically, when the bath temperature is T ° C., the mass% of Fe in the bath needs to be 0.03T-17.6% or more. This corresponds to 2.2% at a bath temperature of 660 ° C.

In the hot dipping process, the cold-rolled steel sheet is usually plated by dipping in a molten metal after recrystallization annealing. In a normal cold rolling process, some iron powder remains on the surface of the steel sheet, but such iron powder reacts with the molten metal in the bath and becomes the same component as the alloy layer. Since iron powder has a large surface area, it reacts quickly, increases the substantial alloy layer, and decreases the workability. From this point of view, it is important to remove iron powder from the surface of the steel sheet when entering the annealing furnace. In the present invention, it is desirable that the amount of iron powder adhesion on the surface when entering the annealing furnace be 0.5 g / m ² or less on one side. Although the washing method is not particularly limited, in order to remove the oil at the same time, electrocleaning in an alkaline solution, combined use of a brush, or the like is usually used.

  In the Al-Si plating bath, 0.001% or more of one or more of Mg, Ca, Sr, Ni, Cu, Ti, Ce, La, Mn, Cr, Co, Mo, Zn, and Sn are included as other elements. % Or less can be added. Elements such as Mg, Ca, Mn, Cr, Ni, Cu, Co, Mo, Zn, and Sn contribute to improving the corrosion resistance of the Al-plated steel sheet, and Sr, Ti, Ce, and La are the dispersion states of Si in Al-Si. Contributes to corrosion resistance. The effect is effective at 0.001% or more, and the addition of 1% or more is not preferable because it involves an increase in the amount of intermetallic compounds floating in a bath called dross, an increase in the melting point, and the like. When these elements are added to the bath, they are distributed in the Al—Si plating layer or alloy layer. In addition, the immersion time in the bath is not particularly limited, but is usually about 1 to 5 seconds in many cases.

  In the Al—Si binary system, since the eutectic point is about 12% Si, it has been conventionally considered that the effect of lowering the bath temperature can be obtained by adding Si. However, in the present invention, in the Al-Si-Fe ternary system in which Fe is contained in the bath in an amount of 1.5% or more, the crystallization temperature of the primary crystal hardly changes in a wide range of Si: 5 to 17%. The knowledge of was also obtained. Therefore, there is no concern that dross generation becomes severe even if the Si amount in the bath is reduced.

  Since the alloy layer of the hot-dip Al-plated steel sheet produced by such a method is composed of an α phase, the amount of Si is 5 to 12% when analyzed. This Si concentration corresponds to the Si concentration of the α phase. The alloy layer thickness is 2.5 μm or less. It is possible to obtain an extremely thin alloy layer of about 1.5 μm by reducing the bath temperature as much as possible within the α-phase generation conditions. The composition of the alloy layer can be analyzed by using instrumental analysis such as EPMA, FE-SEM-EDS from the cross section. However, since the analysis range of these instrumental analyzes is about 1 μm with respect to the thickness of the alloy layer of 2 to 2.5 μm, it should be noted that depending on the analysis site, information on the base iron or Al plating layer is also included.

  As an example, FIGS. 3 and 4 show the analysis results of the cross-sectional structure and composition of the hot-dip Al-plated steel sheet produced by the method according to the present invention. FIG. 3 is a diagram showing a cross-sectional structure and an analysis site of an Al-plated steel sheet by an optical micrograph at 6.5% Si-2% Fe, a bath temperature of 650 ° C., and an intrusion plate temperature of 650 ° C. ) Is an optical micrograph, and FIG. 3B is a diagram showing a cross-sectional structure of the alloy layer from a cross section using FE-SEM-EDS instrumental analysis. FIG. 4 is a diagram showing the results of tissue analysis by FE-SEM-EDS, and the numbers in the figure correspond to the sites shown in FIG.

  The parts 2 to 5 correspond to the alloy layers, and 3 to 5 of these correspond to α or α + L on the ternary phase diagram, and the Si concentration is 8 to 9%. The parts 4 and 5 are considered to be located between the α phase and L (liquid phase) because they include information on the Al plating layer in addition to the α phase. If the alloy layer is β phase, the analytical value should be located at β or β + L, and the alloy layer can be easily identified by such a method. In addition, it can be judged that the part 2 is located on the line which connects the parts 1 and 3, and contains the information of both (alpha) phase and a steel plate (bcc).

Although there is no particular limitation on the cooling process after the Al plating, since the alloy layer continues to grow in the cooling process, it is preferable that the cooling be fast. In this sense, the cooling time to 580 ° C. after plating is preferably 20 seconds or less.
Providing a post-treatment film such as chromate, resin coating, phosphate-based inorganic film on the surface after Al plating does not impair the gist of the present invention. These films have the effect of improving initial rust prevention, workability, weldability, and the like. The plating adhesion amount of the present invention can be about 60 to 250 g / m ^{2 on} both sides, and is the same as that of normal Al plating.

The appearance after the Al-Si plating is spangled unless special treatment is performed. It is also possible to reduce the spangle or to make it inconspicuous by spraying powder of alumina or the like or under pressure by a skin pass.
As the plating base plate of the present invention, those conventionally used can be used, Al-k steel, Ti-IF steel, Ti-Nb-IF steel, medium carbon steel (0.1 to 0.3% C steel). ), Cr-containing steel, Nb-containing steel, low Al-solid solution N-containing steel, and the like. Further, as described above, there are an RTF method and a non-oxidizing furnace method as the Al plating process, and the present invention exhibits the effect in either method.

Next, the present invention will be described in more detail with reference to examples.
Example 1
Steel of the components shown in Table 1 is melted by a normal converter-vacuum degassing treatment to form a steel slab, followed by hot rolling, pickling and cold rolling under normal conditions, and a plate thickness of 1.2 mm A cold-rolled steel sheet was obtained. These steel plates were subjected to Al-Si plating by a non-oxidation furnace-reduction furnace type hot-dip plating line. Cleaning using an alkaline bath and a brush was applied on the front surface of the annealing furnace, and the amount of iron powder adhered at this time was 0.06 g / m ² on one side. The amount of plating adhered was 80 g / m ^{2 on} both sides. In the non-oxidizing furnace, coke gas and air were mixed and burned, and the air ratio (ratio of the amount of supplied air to the amount of air necessary for complete combustion) was set to 0.95. The atmosphere of the reduction furnace was nitrogen-15 vol% hydrogen and the dew point was -30 ° C. The maximum plate temperature is 805 ° C., and the immersion time is 2.6 seconds. At this time, the sample was manufactured by changing the plating bath composition, bath temperature, and penetration plate temperature. The intrusion plate temperature was measured at a position 1 m from the bath, and the plating bath temperature was at a position 500 mm from the bath surface. The cooling after plating was mist cooling, and the cooling time to 580 ° C. was 5 to 15 seconds. The thickness of the alloy layer was measured by observing a cross section of this sample, and the alloy layer was identified at three locations in the visual field by the method described above. Moreover, the plating appearance and plating workability were evaluated by the methods shown below. These relationships are shown in Table 2.

(1) Plating appearance A sample of 100 × 100 mm was sheared, and both sides thereof were observed to count the number of plating defects (usually called non-plating). In the observation, the Al—Si plating layer was peeled off in 20% NaOH and the measurement was performed after exposing the alloy layer, and the average value of both surfaces was calculated. By exposing the alloy layer, it is easy to distinguish between a dark alloy layer and a glossy substrate, and it is also possible to measure a portion where only the Al—Si plating is coated, although the alloy layer is not formed.
[Evaluation criteria]
○: 2 or less non-plating △: 3-5 non-plating ×: 6 or more non-plating

(2) Plating workability A 30 × 300 mm sample was pressure-bonded with a bead drawing die made of SKD11 as shown in FIG. 5 and pulled upward using a tensile tester. When the pressing force was 500 kgf, the thickness reduction was 10 to 13%. The cracked state of the plated layer and the alloy layer when drawn under these conditions was observed with a microscope from a cross section. The observation length was 0.5 mm, and the number of cracks penetrating the Al—Si plating layer during this period was evaluated.
[Evaluation criteria]
○: 1 or less △: 2 to 5 ×: 6 or more

  The steel used here has relatively high amounts of Si and Mn, and is a component that tends to be slightly unplated. No. In 1-6 and 7-10, the bath temperature was kept constant and the amount of Si was changed. Then, when the Si amount was low, the θ phase was generated, and when the Si amount was large, the β phase was generated, and the alloy layer also grew thick. No. Nos. 13 and 14 are cases where the temperature variation in the bath is large and the Fe content in the bath is low, but the alloy layer also tends to grow easily at this time. At this time, both α phase and β phase existed in the alloy layer, and α phase was observed in the lower layer and β phase was observed in the upper layer.

No. 15 and 16 show the influence of the penetration plate temperature. If the penetration plate temperature is too low, dross tends to adhere to the surface, and if the penetration plate temperature is high, the alloy layer tends to grow. When these conditions were appropriate, the alloy layer was 2.5 μm or less, mainly composed of α phase, and showed good appearance and workability.
In Table 2, the type of the alloy layer is determined by composition analysis from a cross section and plotting on a phase diagram. Si: 5 to 12% as the α phase, Si: 12 to 18% as the β phase, and Si: 0 to 3% as the θ phase.

(Example 2)
Steel of the components shown in Table 3 is melted by a normal converter-vacuum degassing treatment to obtain a steel slab, followed by hot rolling, pickling and cold rolling under normal conditions, and a plate thickness of 0.8 mm A cold-rolled steel sheet was obtained. This steel plate was subjected to Al plating under the same conditions as in Example 1. The composition of the plating bath was Al-7% Si-2% Fe, the bath temperature was 650 ° C., the penetration plate temperature was 655 ° C., and the immersion time in the bath was 1.7 seconds. However, the air ratio was adjusted to 1.2 only when passing steel C. The evaluation method and criteria are the same as those in Example 1. As shown in Table 2, when manufactured under these conditions, both the plating appearance and adhesion were good. However, since only steel type C contains about 11% Cr, a tendency of slightly more defects than other steel types was recognized.

(Example 3)
Steel of the component shown in B of Table 3 is melted by a normal converter-vacuum degassing treatment to obtain a steel piece, and then hot rolling, pickling and cold rolling are performed under normal conditions, and the sheet thickness is 0. An 8 mm cold-rolled steel sheet was obtained. This steel plate was subjected to Al plating under the same conditions as in Example 1. However, the amount of iron powder was adjusted to several levels by changing the cleaning conditions before annealing. The composition of the plating bath was Al-7% Si-2% Fe, the bath temperature was 650 ° C., the penetration plate temperature was 655 ° C., and the immersion time in the bath was 1.7 seconds. The evaluation method and criteria are the same as those in Example 1. Table 4 shows the characteristics of the test materials. Moreover, as shown in Table 5, when the adhesion amount of iron powder increased, the reaction product of iron powder and Al plating bath tended to remain on the surface. At this time, cracking of the plating occurred starting from this reaction product.

It is an Al-Fe-Si type | system | group ternary phase diagram in 650 degreeC. It is a figure which shows the relationship between the amount of Si in a bath, bath temperature, and the alloy layer to produce | generate. It is a figure which shows the cross-sectional structure and analysis site | part of Al plating steel plate by an optical microscope photograph. It is a figure which shows the structure | tissue analysis result by FE-SEM-EDS. It is a figure which shows a bead extraction metal mold | die.

Claims (5)

When continuous hot-dip Al plating is applied to a steel sheet, the amount of Si in the Al plating bath (mass%) and the bath temperature (° C) are within the quadrilateral ABCD shown below, and the bath temperature is T ° C. A method for producing a hot-dip Al-plated steel sheet excellent in workability, characterized in that the amount of Fe in the bath is 0.03T-17.6% by mass or more.
A (4.2%, 635 ° C), B (7%, 635 ° C), C (10%, 680 ° C), D (6.5%, 680 ° C) When continuous hot-dip Al plating is performed on a steel sheet, the amount of Si in the Al plating bath (% by mass) and the bath temperature (° C.) are within the pentagonal ABCDE shown below, and the bath temperature is T ° C. A method for producing a hot-dip Al-plated steel sheet having excellent workability, wherein the amount of Fe in the plating bath is 0.03T-17.6% by mass or more.
A (4.2%, 635 ° C), B (7%, 635 ° C), C (9%, 664 ° C), D (9%, 680 ° C), E (6.5%, 680 ° C) The molten Al excellent in workability according to claim 1 or 2, characterized in that the temperature of the penetration of the steel sheet into the bath during continuous hot-dip Al plating on the steel sheet is T-25 ° C or higher and T + 25 ° C or lower. Manufacturing method of plated steel sheet. The workability according to any one of claims 1 to 3, wherein the amount of iron powder adhering to the annealing furnace before continuous molten Al plating is 0.5 g / m ² or less per side. A method for producing an excellent hot-dip Al-plated steel sheet. Excellent in workability, characterized in that the Si amount in the intermetallic compound layer present at the interface between the steel plate and the Al plating layer is 5 to 12% by mass and the average thickness is 2.5 μm or less. Hot-dip Al-plated steel sheet.

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