TWI676508B - Al-based plated steel sheet and method of producing the same - Google Patents

Abstract

An Al-based plated steel sheet characterized in that the average composition of Al contained in the Al-based plating layer is 85% or more by mass%, and Si is 4% or more and 12% or less by mass%. The amount is 30 g / m ² or more, the Si area ratio of the plating surface is 12% or less, the maximum value of the Si concentration distribution in the thickness direction of the Al-based plating layer is 15% or less by mass%, and the thick Al-based plating is The ratio of the maximum value of the Si concentration distribution in the layer thickness direction to the minimum value of the Si concentration when the Fe concentration is 4% by mass or less is 1.0 or more and 2.0 or less.

Description

Al-based plated steel sheet and manufacturing method thereof

The present invention relates to an Al-based plated steel sheet which is capable of sufficiently exhibiting corrosion resistance after painting and is suitable for hot pressing, and a method for producing the same.

In recent years, in order to protect the environment and suppress global warming, the demand for suppressing the consumption of fossil fuels has been increasing, and this demand has affected various manufacturing industries. The automobile industry, which manufactures indispensable means of movement for daily life, has also sought to suppress the consumption of fuel by reducing the weight of the car body without exception. Many automobile parts are made of iron, especially steel plates. Reducing the total weight of the steel plates used is very important for reducing the weight of the car body and suppressing fuel consumption.

However, for automobiles, safety must be ensured, so it is not allowed to reduce the thickness of the steel sheet alone, and it is also required to maintain the mechanical strength of the steel sheet. As mentioned above, the demand for steel plates has gradually increased not only in the automotive industry, but also in various manufacturing industries. Therefore, by increasing the mechanical strength of steel plates, research and development are being performed on steel plates that can maintain or improve the mechanical strength even if the steel plates used in the past are thinned.

In general, materials with excellent mechanical strength tend to have reduced formability and shape freezing properties during forming processes such as bending, and when they are processed into complex shapes, the processing itself is difficult. As one of the means for solving such a problem related to formability, a so-called "hot pressing method (also referred to as a hot stamping method, a hot pressing method, a mold quenching method, and pressure hardening)" can be cited. In this hot pressing method, the material to be formed is first heated to a high temperature (Vostian Iron Zone), and the steel sheet softened by the heating is pressed and formed, and then cooled.

According to this hot pressing method, the material is first heated to a high temperature to soften it, so the material can be easily pressed and processed, and the quenching effect brought by the cooling after forming can be used to improve the mechanical strength of the material. Therefore, by this hot pressing, a molded product having both good shape freezing properties and high mechanical strength can be obtained.

However, when the steel sheet is hot-pressed, if it is heated to a high temperature of, for example, 800 ° C. or higher, iron on the surface is oxidized to generate scale (oxide). Therefore, after the hot pressing, a step of removing scale (a step of removing rust) must be performed, and productivity is reduced. In addition, if a molded product is required to have corrosion resistance, the surface of the molded product is subjected to rust prevention treatment or a metal film is formed after hot pressing. Therefore, a surface purification step or surface treatment step is required, and productivity is further reduced.

An example of suppressing such reduction in productivity is a method of forming a film on a steel sheet. Generally, the film on the steel sheet is made of various materials such as organic materials and inorganic materials. Among them, a zinc-based plated steel sheet, which has a sacrificial anticorrosive effect on a steel sheet, is widely used in automotive steel sheets and the like from the viewpoint of its own corrosion resistance and steel sheet production technology.

However, the heating temperature of hot pressing (700 ° C. to 1,000 ° C.) is higher than the decomposition temperature of the organic material or the boiling point of Zn (zinc). Therefore, when the steel sheet is heated for hot pressing, the plating layer on the surface of the steel sheet may evaporate, and the surface properties may be significantly deteriorated.

Therefore, when hot-pressing, it is desirable to form an Al (aluminum) -based metal film having a higher boiling point than an organic-based material film or a Zn-based metal film, for a steel plate that is heated to a high temperature, to form a so-called Al-based plated steel plate. By forming the Al-based metal film, the scale can be prevented from adhering to the surface of the steel sheet without the need for steps such as a rust-removing step, and thus the productivity is improved. In addition, Al-based metal film also has anti-rust effect, so the corrosion resistance after coating will also be improved.

As described above, in an Al-based plated steel sheet in which an Al-based metal film is formed on a steel having a predetermined steel composition, one of the problems is to improve the workability during hot pressing. Regarding the workability of the hot pressing method, there are some doubtful matters such as that the Fe-Al-Si plating layer generated during heating is hard and may bite into the mold, or may be accumulated in the mold due to a large friction coefficient. Due to these doubtful matters, the surface of the product may be damaged, which may cause the appearance grade to deteriorate.

As one of the means to solve the above-mentioned problems, a method has been proposed in which a coating layer containing zinc oxide (ZnO) is attached to a plating surface (see, for example, Document 1 (International Publication No. 2013/157522) and Document 2 (International Publication 2014/171417), Document 3 (International Publication No. 2009/131233), Document 4 (International Publication No. 2015/087921)).

The methods disclosed in Documents 1 to 4 are specifically methods for attaching a film layer containing a resin component or a silane coupling agent as an adhesive agent to the surface of a steel sheet to suppress ZnO from falling off, and making the adhesive agent during hot pressing Of the organic solvent component was volatilized and only ZnO remained. According to the method, voids generated due to the combustion and evaporation of the organic solvent cause ZnO to come into point contact with the mold metal, and the lubricity is improved.

By forming a ZnO-containing surface on an Al-based plating layer The coating layer will improve the sliding properties during hot pressing. However, recently, because the pressed shape is complicated, the Al-based plating layer is easily peeled off during processing. In addition, in order to improve the workability and extend the life of the material, higher corrosion resistance is required. In particular, when an Al-based plating layer is formed by hot-dip plating, generation of an alloy layer between steel and Al may be a problem. To suppress growth of the alloy layer, Si is added to the plating bath. In ordinary molten Al-based plating, after being pulled up from the plating bath, cooling is performed at 10 ° C./sec. At this time, the surface layer of the plating is non-equilibrium solidified, and is covered by eutectic with Si concentration.

Summary of invention

The present invention has been made in view of the foregoing circumstances, and an object thereof is to provide an Al-based plated steel sheet for hot pressing that can sufficiently exhibit corrosion resistance after coating and a method for producing the same.

The Al-based plated steel sheet in the present invention is an Al-Si-based plated steel sheet, and is a product produced by having a Si concentration in a plating bath of 6 mass% or more and 12 mass% or less. The Si concentration in the entire Al-based plating layer of the plated steel sheet manufactured by this method basically has a composition of 6 mass% or more and 12 mass% or less as the composition of the plating bath.

Generally speaking, if the Al-based plating layer contains Si, the plating-based Al solidifies from the steel sheet side as the primary crystal during the plating step of manufacturing the Al-based plating steel sheet. Therefore, on the surface of the Al-based plating layer, Si is concentrated to a high concentration on the surface side of the final solidification. Fig. 1 shows that after applying a Si-containing Al-based plating to a steel plate by a general method, EPMA (the measuring equipment is JXA8500F made by Japan Electronics Co., Ltd.). The distribution pattern is 500 points × 500 points, and the step interval is 1 μm, beam diameter is 1 μm) to measure the Si area ratio obtained from the surface of the Al-based plating layer. The horizontal axis represents the Si concentration in the plating bath (the Si concentration of the entire Al-based plating layer), and the vertical axis represents the Si surface area ratio on the surface of the Al-based plating layer. As is clear from FIG. 1, compared with the Si concentration of the entire Al-based plating layer, the Si area ratio on the surface is about 3 times as thick.

If the heating conditions are used to hot press an Al-based plated steel sheet containing Si in the Al-based plating layer as described above (furnace temperature 900 ° C or higher and 950 ° C or lower × furnace residence time 0.5 minutes to 6 minutes) To heat, as shown in Figures 2 and 3, five layers with different Al, Si, and Fe concentrations are formed. The first surface layer is an AlFe layer with a thin Si concentration. The second layer (the second layer from the surface of the five layers) is a layer with a high Si concentration. This high Si layer (second layer) shows the highest potential among the five layers, and promotes the cathodic reaction (reduction reaction of dissolved oxygen) of corrosion. Therefore, if this second layer is exposed, there is a tendency to promote corrosion.

In other words, it was found that if the area ratio of Si on the plating surface becomes higher during the plating stage before hot pressing and heating, the second layer with a higher Si concentration will be easily formed during the heating stage of hot pressing. Two layers will form a corrosion circuit with the first layer and the corrosion resistance will deteriorate after coating.

In addition, as described above, in the plating step for manufacturing an Al-based plated steel sheet, the Al-based plating starts to solidify from the steel sheet side, and Si is concentrated to a high concentration on the surface side that is finally solidified. It is found that the Si area ratio in the plating surface increases due to this phenomenon.

It was also found that even when Si is not concentrated on the surface but is internally concentrated, the second layer is formed during hot pressing.

The inventors have found that by removing the Si-concentrated portion after the plating and solidification by pickling, the workability and the corrosion resistance after coating during hot pressing are significantly improved.

Based on the above knowledge, the present inventors have completed the invention. The gist is as follows.

[1]. An Al-based plated steel sheet characterized in that the average composition of Al contained in the Al-based plating layer is 85% or more by mass%, and Si is 4% or more and 12% or less by mass% , The plating adhesion amount is 30 g / m ² or more, the Si area ratio of the plating surface is 12% or less, the maximum value of the Si concentration distribution in the thickness direction of the Al-based plating layer is 15% or less by mass%, and Al The ratio of the maximum value of the Si concentration distribution in the thickness direction of the plating layer to the minimum value of the Si concentration when the Fe concentration is 4% by mass or less is 1.0 or more and 2.0 or less.

[2]. The Al-based plated steel sheet according to [1], wherein the surface roughness of the aforementioned Al-based plated layer is 0.1 μm or less based on the arithmetic average roughness Ra.

[3]. The Al-based plated steel sheet according to [1] or [2], wherein the maximum Si concentration distribution in the thickness direction of the aforementioned Al-based plating layer and the minimum Si concentration when the Fe concentration is 4% by mass or less The value ratio is 1.0 ~ 1.5.

[4]. The Al-based plated steel sheet according to any one of [1] to [3], comprising a surface coating layer provided on the Al-based plating layer and containing ZnO particles and organic resin, and the deposition amount of ZnO to Zn metal particles in terms of 0.5g / m ² or more and ² or less at 10.0g / m. [5]. A method for manufacturing an Al-based plated steel plate, characterized in that the following steps are performed: a plating step of immersing the steel plate in an Al plating bath containing Si in an amount of 6% to 15% by mass, To form a plating layer; a cooling step to cool the aforementioned steel sheet after immersion; an etching step to immerse the cooled steel sheet in an acidic solution below pH 1 to etch the surface layer to the following depth: the Si area ratio of the plating surface Below 12%, the maximum value of the Si concentration distribution in the thickness direction of the Al-based plating layer is 15% or less in terms of mass%, and the maximum value of the Si concentration distribution in the thickness direction of the Al-based plating layer and the Fe concentration are 4 mass The ratio of the minimum value of the Si concentration at% or less is 1.0 or more and 2.0 or less.

According to the present invention, it is an object of the present invention to provide an Al-based plated steel sheet for hot pressing that can sufficiently exhibit corrosion resistance after coating and a method for manufacturing the same.

Hereinafter, embodiments of the Al-based plated steel sheet of the present invention (hereinafter sometimes referred to simply as "steel sheet"), which is preferable for hot pressing, will be described in detail. However, the following embodiments are not limited to the present inventors. In addition, the constituent elements of the above-mentioned embodiment include elements that can be easily replaced by those with ordinary knowledge in the technical field to which they belong, or substantially the same elements. In addition, those having ordinary knowledge in the technical field can arbitrarily combine various forms included in the above-mentioned embodiments within a scope that is obvious.

An example of the Al-based plated steel sheet 100 of the present invention is shown in FIG. 4. The Al-based plated steel sheet 100 of the present invention is configured by forming an Al-based plated layer 103 on the surface of a base material 101. Alternatively, as shown in FIG. 5, a surface coating layer 107 is further formed on the surface of the Al-based plating layer 103, and the surface coating layer 107 is composed of ZnO particles 109 bonded by an organic resin 111. Each layer is described in detail below. However, FIGS. 4 and 5 are examples in which an Al-based plating layer 103 and a surface coating layer 107 are formed on one side of the Al-based plated steel sheet 100, but they may be formed on both sides. <Al-based plated steel sheet 100> [Base material 101]

The base material 101 (the member used to form the Al-based plating layer 103) for the Al-based plated steel sheet 100 of this embodiment is used even if it is hot-pressed after the plating layer is formed. Refers to various properties related to mechanical deformation and damage such as tensile strength, yield point, elongation, depth of penetration, hardness, impact value, fatigue strength, creep strength, etc.). For example, a member having a hardenability improved by adding C (carbon) or an alloy element is used. Thereby, an automotive component obtained by hot-pressing an Al-based plated steel sheet 100 prepared by forming an Al-based plated layer 103 and a surface coating layer 107 described later can exhibit excellent mechanical strength.

That is, as long as the base material 101 for the Al-based plated steel sheet 100 of the present embodiment has excellent mechanical strength, a well-known thing can be used. As the base material 101, for example, a material having the following components can be used, but the components of the base material 101 are not limited thereto.

The base material 101 in the present embodiment contains, for example, mass: C: 0.01% or more and 0.5% or less, Si: 2.0% or less, Mn: 0.01% or more and 3.5% or less, P: 0.1% or less, and S: 0.05% or less. , Al: 0.001% or more and 0.1% or less, N: 0.01% or less, and optionally one or more of the following elements: Ti: 0.005% or more and 0.1% or less, B: 0.0003% or more and 0.01% or less Below, Cr: 0.01% or more and 1.0% or less, Ni: 0.01% or more and 5.0% or less, Mo: 0.005% or more and 2.0% or less, Cu: 0.005% or more and 1.0% or less, and may further contain W, V, and Nb , Sb and other elements, and the remainder is composed of Fe and unavoidable impurities. Hereinafter, each component added to the base material 101 will be described in detail. In the following description, the unit% of each component refers to mass%. (C: 0.01% or more and 0.5% or less)

Carbon (C) is unavoidably contained in steel, and is contained to ensure the mechanical strength of the base material 101 for the purpose. Excessively reducing the C content will increase the smelting cost, so it is preferable to contain more than 0.01%. In addition, if the C content is 0.1% or more, it becomes unnecessary to add a large amount of other alloy elements in order to improve the mechanical strength, so the effect of increasing the strength by adding C is large. On the other hand, if the C content is more than 0.5%, the base material 101 can be hardened more, but melt cracking easily occurs. Therefore, C is preferably contained in an amount of 0.01% or more and 0.5% or less, and from the viewpoint of improving strength and preventing melt fracture, it is more preferable to add C in an amount of 0.1% to 0.4%. The C content is more preferably 0.15% to 0.35%. (Si: 2.0% or less)

Silicon (Si) is an element which is added as a deoxidizer and cannot be avoided during the refining of steel. However, excessive addition of Si may cause a reduction in ductility in a hot-rolling step at the time of steel sheet production, or as a result, may deteriorate surface properties. Therefore, it is preferably set to 2.0% or less.

In addition, Si is one of the reinforcing elements that can increase the mechanical strength of the base material 101, and it may be added to ensure the same mechanical strength as C. If the Si content is less than 0.01%, it is difficult to exert the effect of increasing the strength, and it is difficult to obtain a sufficient increase in mechanical strength. On the other hand, Si is also an easily oxidizable element. Therefore, when the Si content is more than 0.6%, the wettability is reduced when molten Al-based plating is performed, and there is a possibility that unplating may occur. Therefore, Si is preferably added at a content of 0.01% to 0.6%. The Si content is more preferably set to 0.05% or more and 0.5% or less. (Mn: 0.01% or more and 3.5% or less)

Manganese (Mn) is an element which cannot be avoided during the refining process of steel, such as being added as a deoxidizer. However, excessive addition of Mn may impair the uniformity of quality due to Mn segregation during casting, and the steel sheet may be excessively hardened, resulting in a reduction in ductility during hot working and cold working. Therefore, it should be set to 3.5% or less. On the other hand, if the Mn content is reduced to less than 0.01%, the step or cost of removing Mn will increase, so the Mn content should be more than 0.01%. Therefore, Mn is preferably set to 0.01% to 3.5%.

In addition, Mn is one of the strengthening elements of the base material 101 and one of the elements that can improve the hardenability. Furthermore, Mn is also effective in suppressing the thermal brittleness caused by S (sulfur), which is one of the unavoidable impurities. Therefore, by setting the Mn content to 0.5% or more, the effect of improving hardenability or suppressing hot brittleness can be obtained. On the other hand, if the Mn content is more than 3%, the residual γ phase may become excessive and the strength may be reduced. Therefore, Mn is preferably added at a content of 0.5% to 3%. The Mn content is more preferably 1% or more and 2% or less. (P: 0.1% or less)

Phosphorus (P) is an element that cannot be avoided, on the other hand, it is a solid solution strengthening element, and it is an element that can increase the strength of the base material 101 relatively inexpensively. However, based on the economic refining limit, the lower limit of the content should be set to 0.001%. On the other hand, if the P content is more than 0.1%, the toughness of the base material 101 may decrease. Therefore, the P content is more preferably 0.001% to 0.1%. The P content is more preferably 0.01% to 0.08%. (S: 0.05% or less)

Sulfur (S) is an unavoidable element, and as MnS, it becomes an inclusion in the base material 101 and becomes a starting point of destruction, which hinders ductility and toughness and becomes a cause of deterioration of workability. Therefore, the lower the S content, the better, and the upper limit of the content should be set to 0.05%. On the other hand, in order to reduce the S content, an increase in manufacturing costs can be expected, so the lower limit of the content should be 0.001%. The S content is more preferably 0.01% to 0.02%. (Al: 0.001% or more and 0.1% or less)

Aluminum (Al) is a component contained in the base material 101 as a deoxidizer, but it is also an element that hinders plating properties. Therefore, the upper limit of the Al content should be set to 0.1%. On the other hand, the lower limit of the Al content is not particularly specified, but is preferably set to, for example, 0.001% based on the economical refining limit. The Al content is more preferably 0.01% to 0.08%. (N: 0.01% or less)

Nitrogen (N) is an unavoidable element. From the viewpoint of stabilizing various characteristics of the base material 101, its content should be fixed. Specifically, it can be fixed according to the content of elements such as Ti and Al. On the other hand, if the content of N is too large, since the content of Ti, Al, etc. will increase and the manufacturing cost of the base material 101 can be expected to increase, the upper limit of the content of N should be set to 0.01%. (Ti: 0.005% or more and 0.1% or less, B: 0.0003% or more and 0.01% or less, Cr: 0.01% or more and 1.0% or less, Ni: 0.01% or more and 5.0% or less, Mo: 0.005% or more and 2.0% or less , Cu: 0.005% or more and 1.0% or less or 1 or more) (Ti: 0.005% or more and 0.1% or less)

Titanium (Ti) is one of the strengthening elements of the base material 101 and is an element that can improve the heat resistance of the Al-based plating layer 103 formed on the surface of the base material 101. If the Ti content is less than 0.005%, the effect of improving strength or heat resistance cannot be sufficiently obtained. On the other hand, if Ti is excessively added, carbides or nitrides are formed, for example, and the base material 101 may be softened. In particular, if the Ti content is more than 0.1%, there is a high possibility that the intended mechanical strength cannot be obtained. Therefore, Ti is preferably added at a content of 0.005% to 0.1%. The Ti content is more preferably 0.03% or more and 0.08% or less. (B: 0.0003% or more and 0.01% or less)

Boron (B) is an element that acts during quenching and has the effect of increasing the strength of the base material 101.

If the B content is less than 0.0003%, the above-mentioned effect of increasing the strength cannot be obtained sufficiently. On the other hand, if the B content is more than 0.01%, inclusions (for example, BN, boron carbide, etc.) are formed in the base material 101 and become brittle, which may reduce the fatigue strength. Therefore, B should be added at a content of 0.0003% or more and 0.01% or less. The B content is more preferably 0.001% to 0.008%. (Cr: 0.01% or more and 1.0% or less)

Chromium (Cr) suppresses formation of an Al-based plating layer by forming the Al-based plating layer 103 at the interface with the base material 101 when the Al-based plating layer 103 is alloyed to form an Al-Fe alloy layer. Effect of AlN generation due to 103 peeling. In addition, Cr is one of the elements that can improve the wear resistance and one of the elements that can improve the hardenability. If the Cr content is less than 0.01%, the above effects cannot be sufficiently obtained. On the other hand, if the Cr content is more than 1.0%, not only the above-mentioned effects will be saturated, but also the manufacturing cost of the steel sheet will increase. Therefore, Cr is preferably added at a content of 0.01% to 1.0%. The Cr content is more preferably 0.5% to 1.0%. (Ni: 0.01% or more and 5.0% or less)

Nickel (Ni) has the effect of improving the hardenability during hot pressing. In addition, Ni has the effect of improving the corrosion resistance of the base material 101. However, if the Ni content is less than 0.01%, the above effects cannot be sufficiently obtained. On the other hand, if the Ni content is more than 5.0%, not only the above-mentioned effects will be saturated, but also the manufacturing cost of the steel sheet will increase. Therefore, Ni is preferably added at a content of 0.01% to 5.0%. (Mo: 0.005% or more and 2.0% or less)

Molybdenum (Mo) has the effect of improving hardenability during hot pressing. In addition, Mo also has the effect of improving the corrosion resistance of the base material 101. However, if the Mo content is less than 0.005%, the above effects cannot be sufficiently obtained. On the other hand, if the Mo content is more than 2.0%, not only the aforementioned effects will be saturated, but also the manufacturing cost of the steel sheet will increase. Therefore, Mo is preferably added in an amount of 0.005% to 2.0%. (Cu: 0.005% or more and 1.0% or less)

Copper (Cu) has the effect of improving the hardenability during hot pressing. Cu also has the effect of improving the corrosion resistance of the base material 101. If the Cu content is less than 0.005%, the above effects cannot be sufficiently obtained. On the other hand, if the Cu content is more than 1.0%, not only the above-mentioned effects will be saturated, but also the manufacturing cost of the steel sheet will increase. Therefore, Cu should preferably be added in an amount of 0.005% to 1.0%. (W, V, Nb, Sb)

In addition to the above-mentioned many elements, the base material 101 of the present embodiment can optionally add elements such as tungsten (W), vanadium (V), niobium (Nb), and antimony (Sb). As long as these elements are added in a known range, any of them may be used. (The remaining part)

The remainder of the base material 101 is only iron (Fe) and unavoidable impurities. The unavoidable impurities refer to the components contained in the raw materials or the components mixed in the manufacturing process, and the components that are not the components intentionally contained in the base material 101.

The base material 101 formed by the above components is quenched by heating such as hot pressing, and can have a mechanical strength of about 1500 MPa or more. Although it is a steel sheet with excellent mechanical strength like this, if it is processed by hot pressing, it can be pressed in a softened state by heating, so it can be easily formed. In addition, after pressing, the base material 101 cooled from a high temperature can achieve high mechanical strength, and even if the thickness is reduced for weight reduction, the mechanical strength can be maintained or even improved. [Al-based plating layer 103]

The Al-based plating layer 103 is formed on at least one side of the base material 101. In the Al-based plating layer 103, Si is added as an element that suppresses the formation of the Fe-Al alloy layer during hot-dip plating. If the Si content in the Al-based plating layer 103 is less than 4% by mass, the Fe-Al alloy layer excessively grows during the hot-dip plating, and thus the cracking of the plated layer is promoted during the pressing process. On the other hand, when the Si content is more than 12% by mass, even if the amount of Si on the surface is reduced, the workability and corrosion resistance of the Al-based plating layer 103 are still reduced. Therefore, the Si content in the Al-based plating layer 103 is set to 4% by mass or more and 12% by mass or less. The Si content in the Al-based plating layer 103 is more preferably 4% by mass or more and 10% by mass or less. The Al-based plating layer 103 only needs to contain 85% by mass or more of Al. The components other than Al and Si are not particularly limited, but Zn will evaporate due to heating before hot pressing, so it is preferably 10% by mass or less, and should not be contained in an amount greater than the amount of unavoidable impurities. In addition, Fe is also contained due to alloying with Fe in the base material. In addition, it is preferably an Al-Si-based alloy such as JIS 4000 series aluminum alloy, which is an unavoidable impurity other than Al and Si. (It is an Al alloy composed of Al and Si, and is an unavoidable impurity other than Al, Si. Aluminum alloy).

The Si content referred to here is an average composition.

The Al-based plating layer 103 containing 80% by mass or more of Al can prevent corrosion of the base material 101. In addition, the Al-based plating layer 103 can prevent scale (oxide of iron) from being formed on the surface of the steel sheet during heating before hot pressing. Therefore, since the Al-based plating layer 103 is present on at least one side of the base material 101, the scale removal step, the surface purification step, the surface treatment step, and the like can be omitted, and the productivity of automobile parts and the like can be improved. In addition, the Al-based plating layer 103 has a higher melting point than a film of an organic-based material or a film of another metal-based material (for example, a Zn-based material), so that it can be processed at a high temperature during hot pressing.

In addition, an Al oxide-based passivation film is formed on the surface of the Al-based plating layer. This passivation film prevents ZnO from being reduced and disappeared by components in the Al-based plating layer during hot pressing.

In addition, a part of Al contained in the Al-based plating layer 103 is alloyed with Fe in the base material 101 during hot-dip plating or hot pressing. Therefore, the Al-based plating layer 103 is not necessarily formed as a single layer with a fixed composition, but may also be a layer containing a locally alloyed layer (alloy layer) or a steel-aluminum inclined alloy layer whose concentration gradient changes from the surface. Things. (Plating deposit)

The adhesion amount of the Al-based plating layer 103 is 30 g / m ² or more. When it is less than 30 g / m ² , the thickness of the plating becomes too thin, and rust is generated during hot pressing, which deteriorates the corrosion resistance. It is preferably 50 g / m ² or more. (Si area ratio of the surface of the Al-based plating layer 103)

As described above, if the Al-based plating layer 103 is formed by non-equilibrium solidification, Si is easily surface-concentrated. If Si is concentrated on the plating surface during the plating stage before hot pressing and heating, and the Si area ratio becomes high, the second layer with a high Si concentration will be easily formed in the hot pressing and heating stage. The second layer will form a corrosion circuit with the first layer and the corrosion resistance will deteriorate after coating.

In addition, in the plating stage before hot pressing heating, if Si is concentrated on the plating surface and the Si area ratio becomes high, the formation of an Al oxide-based passivation film becomes insufficient. At this time, ZnO may be reduced and disappeared by components in the Al-based plating layer.

Therefore, the Si area ratio on the surface of the Al-based plating layer 103 must be 12% or less. In order to obtain a significant effect, the Si area ratio is preferably 8% or less, and more preferably 6% or less. The lower limit of the Si area ratio is not particularly limited. Although the ideal Si area ratio is 0%, the practical lower limit is 1%.

The Si area ratio on the surface of the Al-based plating layer 103 can be measured by area analysis after EPMA (Electron Probe Micro Analyzer) or area analysis by Auger Electron Spectroscopy (AES) after plating. In this case, if it is EPMA, the measurement equipment is JXA8500F made by Japan Electronics, and the measurement point is 500 points × 500 points, and the measurement is performed at a pitch of 1 μm and the beam diameter is 1 μm. The measurement is preferably performed with a beam diameter of 10 μm or less, a measurement point of 500 points × 500 points, and a 10 μm pitch in a 5 mm × 5 mm field of view. The Si area ratio can also be determined from the Si concentration (atomic%) in a very thin region in the depth direction from the surface. If the surface coating layer 107 described later is formed, when the Si area ratio of the surface of the Al-based plating layer 103 is to be measured later, the depth-wise quantitative analysis can also be performed from the surface by high-frequency glow discharge spectrometry (high-frequency GDS). And set it as follows.

In the high-frequency glow discharge spectroscopic analysis method (high-frequency GDS), it is suitable to measure a diameter of 4mm. A high-frequency GDS is used to specify a portion of the plating component other than Al and Si with a content of 5 element% as the plating surface. After determining the concentration of each constituent component (atomic%) in the portion, the component is determined based on the constituent components. The specific gravity and the atomic weight (molecular weight) were used to calculate the volume fraction of Si. From the viewpoint of quantitative histology, the volume fraction is equal to the area ratio, so the volume fraction of Si obtained in the foregoing manner is the Si area ratio.

As a method of reducing the Si area ratio of the surface of the Al-based plating layer 103, there is a method of etching the surface after plating to remove a portion where Si is concentrated.

For example, if the cooling rate near the solidification temperature is set to 10 ° C / sec to condense Si, the Si-concentrated eutectic on the surface is dissolved in an acidic solution with a pH of 1 or less, and the Si area ratio on the surface can be reduced to 10%. about. In addition, when the cooling rate during solidification is set to 20 ° C./sec, the eutectic Si concentration becomes 20% or more. If this part is dissolved in an acidic solution, the Si area ratio can be reduced to 8% or less.

As a method of etching the surface after plating to remove a portion where Si is concentrated, a method of etching the surface of the Al plating layer with an acid such as sulfuric acid can be exemplified. (Si concentration distribution in thickness direction)

The maximum value of the Si concentration distribution in the thickness direction of the Al-based plating layer 103 is 15% or less (preferably 12% by mass or less) in terms of mass%, and the maximum value of the Si concentration distribution in the thickness direction and the Fe concentration are 4 mass The ratio of the minimum value of the Si concentration at% or less is 1.0 or more and 2.0 or less, and the reason described above is as follows.

First, if the surface area ratio of Si is high, as shown in FIG. 6, a high Si concentration portion is generated in the surface layer, and it becomes easy to form a second layer with a high Si concentration during the heating stage of hot pressing. Before description.

On the other hand, even if there is a part with a high Si concentration not in the surface layer but in the interior as shown in the upper part of FIG. 7, in the heating stage of hot pressing, it will become easy to generate a high Si concentration as shown in the lower part of FIG. Layer 2.

Therefore, as shown in the middle part of FIG. 8, not even the surface but the inside may have a portion having a high Si concentration.

This is the reason for specifying the Si concentration distribution in the thickness direction. The reason for using the Si concentration at a Fe concentration of 4% by mass or less as a minimum value is to consider that the interface between the plating layer and the base material may be alloyed.

The ratio of the maximum value of the Si concentration distribution in the ideal thickness direction to the minimum value of the Si concentration when the Fe concentration is 4% by mass or less is 1.0 to 1.5.

The Si concentration distribution in the thickness direction can be obtained by analyzing the composition of the vertical section of the Al-plated steel sheet using EPMA or the like.

A method for obtaining such a concentration distribution may be a method of etching a surface. For example, if the Si in the plating layer exhibits a concentration distribution as shown in the upper section of FIG. 8, as long as the plating layer is removed by etching to a position where the Si concentration of the surface layer is 15% or less, it will become as shown in the figure. The concentration distribution shown in the middle 8 section. With this concentration distribution, as shown in the lower stage of FIG. 8, after the hot pressing, a second layer having a high Si concentration is not formed in the plating layer.

The etching solution is not particularly limited as long as it is an acidic solution having a pH of 1 or less to which an iron-based inhibitor is added, and examples thereof include an H ₂ SO ₄ aqueous solution having a concentration of 2 mol% or more of the iron-based inhibitor. If it is an acidic solution with a pH greater than 1, the etching may not proceed, or even if it does, the etching rate may be too slow and productivity may deteriorate.

In addition, the following method can be exemplified: immersion in other etching solution, that is, an alkali solution of an aqueous sodium hydroxide solution having a concentration of 2 mol% or more, dissolving the plated metals Al and Si, and then dissolving the remaining Al-Si with the above acid solution -Fe alloy layer.

The etching time is a time when a portion having a high Si concentration can be removed and the adhesion amount of the plating becomes 30 g / m ² or more. Specifically, etching is performed to a depth where the Si area ratio of the plating surface is 12% or less, and the maximum value of the Si concentration distribution in the thickness direction of the Al-based plating layer is 15% or less by mass%, and The ratio of the maximum value to the minimum value is 1.0 or more and 2.0 or less. The plated steel sheet of the present invention can be obtained by, for example, immersing a plated steel sheet having a plating adhesion of 50 g / m ² in a 10% sulfuric acid solution at 60 ° C. for 30 to 60 seconds. And by controlling the temperature or the sulfuric acid concentration of the immersion liquid, the immersion treatment time can be shortened. In addition, the plating surface can be ground to remove the Si-concentrated layer on the surface.

In order not to form a portion with a high Si concentration inside the Al-based plating layer 103, there is also a method in which the cooling conditions after the immersion of the plating bath are set to 15 ° C / sec or less. (Surface roughness)

The surface roughness of the Al-based plating layer 103 is preferably 0.1 μm or less in terms of the arithmetic average roughness Ra. When it is larger than 0.1 μm, the surface unevenness may become too large and a locally thin area may be generated, and there is a concern that rust may be generated during hot pressing. In addition, when the surface film layer 107 is provided, a locally thin area is also generated, and the effect as the surface film layer 107 cannot be sufficiently obtained.

The ideal surface roughness is 0.1 μm or less in terms of the arithmetic average roughness Ra. [Surface coating layer 107]

In order to further improve the thermal lubricity during hot pressing, a surface film layer 107 containing ZnO particles 109 is formed on the surface of the Al-based plating layer 103 of the Al-based plated steel sheet 100.

The surface coating layer 107 preferably contains, for example, ZnO particles 109 and organic resin 111 having an average particle size of 0.10 μm to 5.00 μm, and the adhesion amount of the ZnO particles 109 is 0.5 g / m ^{2 to} 10.0 in terms of metal Zn. g / m ² or less. When an Al-based plating layer 103 is formed on both sides of the base material 101, a surface film layer 107 can be formed on the plating layer on at least one side.

The surface film layer 107 can be formed using a liquid obtained by mixing the above components in various solvents such as water or an organic solvent. (ZnO particles 109)

In order to obtain good thermal lubricity during hot pressing, on the Al-based plating layer 103, the ZnO particles 109 having an average particle size of 0.10 μm or more and 5.00 μm or less are preferably 0.5 g / m ² or more and 10.0 g in terms of metal Zn. / m ² or less. The ZnO particles 109 will come into point contact with the mold, resulting in a reduction in the dynamic friction coefficient and an improvement in thermal lubricity. However, if the average particle diameter of the ZnO particles 109 is less than 0.10 μm, there will be too many contact points between the ZnO particles 109 and the mold during press processing, and the thermal lubricity will not be sufficiently improved.

On the other hand, if the average particle diameter of the ZnO particles 109 is larger than 5.00 μm, the weldability is deteriorated. Although ZnO is insulating, when the particle diameter is small, it will be crushed during welding and pressurization, which can sufficiently ensure the energization point. However, if the average particle diameter of the ZnO particles 109 becomes larger than 5 μm, the ZnO particles 109 become difficult to be crushed during welding and pressing. As a result, the energization point cannot be sufficiently secured and dust is easily generated, so that the weldability is deteriorated.

The method for measuring the average particle diameter of the ZnO particles 109 is not particularly limited. For example, a scanning electron microscope (SEM, Scanning Electron Microscope) or the like may be used to observe arbitrary 10 or more ZnO particles 109 at 2000 times, measure the maximum particle size of each particle, and calculate the average value. Alternatively, the average particle diameter of the ZnO particles 109 may be determined using a particle size distribution measuring device.

In addition, if the adhesion amount of all the ZnO particles 109 in the surface coating layer 107 is less than 0.5 g / m ² in terms of metal Zn, sufficient lubricity cannot be obtained during hot pressing.

The amount of ZnO particles 109 deposited on the Al-based plating layer 103 can be measured by a calibration curve method using XRF (X-ray Fluorescence).

The term "adhesion amount" used herein refers to the amount of adhesion before being placed on a conveyor belt and heated during hot pressing. (Organic resin 111)

The organic resin 111 as a component of the surface film layer 107 is not particularly limited as long as it can function as a binder that holds the ZnO particles 109 in the film. This is because the organic resin 111 burns and disappears during heating before hot pressing, and does not affect subsequent processing such as pressing processing or welding. When the organic resin 111 is a water-based agent, a cationic resin that is weakly alkaline and stable like ZnO is preferably used. For example, a cationic urethane resin or a cationic acrylic resin can be used. The concentration (g / kg) ratio of the organic resin in the pharmaceutical is not particularly specified. The resin usable as the organic resin 111 is a cationic urethane resin (manufactured by Daiichi Kogyo Co., Ltd., product name SUPERFLEX650), and the like.

In order for the organic resin 111 to fully exhibit its role as an adhesive, it is preferable to provide the organic resin 111 with a content of 10% or more and 60% or less with respect to the entire surface coating layer 107 in terms of mass%. If the content is less than 10%, the effect as an adhesive cannot be fully exhibited, and the coating film before heating becomes easily peeled. In addition, in order to stably obtain the effect as an adhesive, the above-mentioned content of the organic resin 111 is more preferably 15% or more. On the other hand, if the content of the organic resin 111 is more than 60%, it becomes obvious that an unpleasant odor is generated during heating.

The method for forming the surface coating layer 107 on the Al-based plating layer 103 is not particularly limited. The surface film layer 107 can be formed by applying an aqueous solution or a solvent obtained by dissolving each of the main components described above to the Al-based plating layer 103 by a well-known method such as a roll coater or a sprayer, and drying it. In addition, when the surface coating layer 107 is formed, the drying method after coating is not particularly limited, and various methods such as hot air, IH (induction heating), NIR (near infrared), and electric heating can be used. In addition, for the heating temperature during drying, the glass transition temperature (Tg) of the organic resin 111, which is a binder, should be appropriately set. ＜ Manufacturing method ＞

Here, the manufacturing method of the Al-based plated steel sheet 100 of the present invention will be briefly described.

First, a steel plate is immersed in an Al plating bath containing Si in an amount of 6% to 15% by mass to form a plating layer (plating step).

The conditions of the base material are the same as those described in [Base Material 101].

Next, the steel sheet after the immersion is cooled (cooling step). Cooling should be air-cooled. This is because if the water mist is used for cooling, the surface roughness will become too large, and the amount of plating to be removed during etching will increase. The cooling rate is not particularly limited, but it is preferably 5 to 15 ° C / second.

Next, the aforementioned steel sheet after cooling is immersed in an acidic solution having a pH of 1 or less, and the surface layer is etched to the following depth: the Si area ratio of the plating surface is 12% or less, and the Si concentration distribution in the thickness direction of the Al-based plating layer The ratio of the maximum value by mass% is 15% or less, and the ratio of the maximum value of the Si concentration distribution in the thickness direction of the Al-based plating layer to the minimum value of the Si concentration when the Fe concentration is 4% by mass or less is 1.0 or more and less than 2.0 or less (etching step).

The reason for specifying the etching conditions is as described in (Si concentration distribution in the thickness direction).

As described above, according to the Al-based plated steel sheet 100 (steel sheet) of the present invention, the Si area ratio on the surface of the Al-based plated layer 103 can be suppressed, thereby suppressing the formation of a high Si concentration in the heating stage of hot pressing. Two layers to prevent deterioration of corrosion resistance after coating after hot working. In addition, according to the Al-based plated steel sheet 100 of the present embodiment to which the surface film layer 107 is added, the presence of the surface film layer 107 having excellent lubricity can suppress adhesion to the mold. Even if the Al-based plating layer 103 is pulverized by heating, the presence of the surface film layer 107 having excellent lubricity can prevent powder (Al-Fe powder, etc.) from adhering to the mold used for subsequent pressing. Therefore, when the steel sheet of this embodiment is hot-pressed, there is no need to remove the Al-Fe powder adhering to the mold and the like, and excellent productivity can be achieved.

Examples Hereinafter, the effects of the present invention will be described more specifically with reference to the invention examples. However, the present invention is not limited only to the conditions used in the following invention examples.

An Al-based plating layer 103 was formed on both sides of the cold-rolled steel sheet (plate thickness of 1.4 mm) using the chemical composition shown in Table 1 (the remainder was Fe and unavoidable impurities) by the Senzimir method. The annealing temperature when forming the Al-based plating layer 103 is about 800 ° C. In the Al-based plating bath, Si is added in an amount of 0% to 19% by mass, and Fe is eluted from the base material 101. After the Al-based plating layer 103 was dissolved in an aqueous solution of hydrochloric acid to which an inhibitor was added, the amount of Si in the Al-based plating layer 103 in the solution was measured by high-frequency inductively coupled plasma emission spectrometry (ICP), and it was confirmed that The amounts are shown in Table 2. [Table 1]

The adhesion amount of the Al-based plating layer 103 to the base material 101 was adjusted to 160 g / m ^{2 on} one side by a gas wiping method. The average cooling rate in the plating solidification temperature zone (solidification temperature ± 20 ° C), sample numbers 1 to 18, 20 to 22, 24, 25, 28 to 33 are at 10 ° C / sec, and sample numbers 19, 23 It was performed at 22 ° C / sec. Sample Nos. 1 to 13 were obtained after forming the aforementioned Al-based plating layer 103, and were not subjected to a dissolution treatment by pickling after solidification of the plating. On the other hand, for sample numbers 14 to 25, after cooling the base material 101 on which the Al-based plating layer 103 was formed, it was immersed in a 10% sulfuric acid solution for 30 seconds, and sample number 28 was immersed for 300 seconds. Sample number 29 was immersed for 250 seconds, sample number 30 was immersed for 200 seconds, sample number 31 was immersed for 150 seconds, sample number 32 was immersed for 15 seconds, and sample number 33 was immersed for 5 seconds.

Sample No. 26 is water mist-cooled, and uses TiO particle suspension to accelerate the coagulation rate by coagulation nucleation of particles and rapid cooling with an aqueous solution to promote coagulation.

Sample No. 27 was also water mist-cooled, and VO particle suspension was used. The coagulation nucleation of particles and rapid cooling with an aqueous solution were used to accelerate the coagulation rate and promote coagulation.

Sample No. 34 is water mist cooling using distilled water.

The Si area ratio on the surface of the Al-based plating layer 103 was measured by AES region analysis.

Thereafter, a surface coating layer 107 is formed. To form the surface coating layer 107, a solution was prepared by mixing and adjusting ZnO particles 109 and organic resin 111 in a solvent, and applying the solution to the Al-based plating layer 103, and applying the solution at a plate temperature of 80 ° C. dry. As described above, the Al-based plated steel sheet 100 of each test example was prepared.

Next, various characteristics and the like of the steel sheets of each test example produced as described above were evaluated by the following methods. (1) Plating thickness

The arithmetic average roughness Ra was measured using a three-dimensional roughness meter (product name: SURFCOM 1900DX-3DF-12) manufactured by Tokyo Precision Co., Ltd. The measurement distance was set to 30 mm, and the average of three measurement points was used as the plating thickness. (2) Plating adhesion

The mass of the steel sheet of each test example before and after plating was measured in accordance with JIS H 8672, and the value obtained by dividing the difference in mass by the area of the sample was the plating adhesion amount g / m ² . (3) Si area ratio

The Si area ratio on the surface of the Al-based plating layer 103 was determined by performing area analysis of EPMA (Electron Probe Micro Analyzer) in a field of view of 5 mm × 5 mm using JXA8500F manufactured by Japan Electronics after plating. At this time, the measurement points were 500 points × 500 points, and the measurement was performed at a pitch of 10 μm and a beam diameter of 10 μm. (4) Si concentration

The steel plates of each test example cut out to a width of 50 mm by a length of 50 mm were immersed in a 10% sulfuric acid aqueous solution prepared by adding a 0.5% by mass inhibitor (HIBIRON Y-30 manufactured by Sugiura Chemical Industries) to dissolve the plating. The dissolved solution was quantitatively analyzed, and the Si concentration was measured by a calibration curve method.

A high-frequency GDS is used to convert the Si intensity into the Si concentration depth distribution map, and set the maximum value to the maximum value of the Si concentration distribution in the thickness direction of the plating, and set the minimum Fe concentration in the area below 4% by mass. The value is the minimum value of the Si concentration distribution in the plating. Find the ratio of the maximum value to the minimum value as the maximum value / minimum value. (5) Alloy layer thickness

Each test example steel plate cut out into a width of 10 mm × length of 30 mm was embedded in a resin, and then the cross section was ground to observe the vertical cross section in the longitudinal direction. After selecting any 20 points in a 20 mm width and measuring the thickness of the alloy layer, the average value of the 20 points was taken as the thickness of the alloy layer. (6) Stripping rate of alloy layer

In the tensile test, each test example steel plate having a width of 30 mm and a length of 300 mm was processed to have an elongation of 10% in the L direction. Then, a sample was cut from the central portion of the L direction to a width of 10 mm and a length of 30 mm and was embedded in the resin. Cross section and observed the vertical cross section in the L direction. The width of the peeling part of the alloy layer spread over a width of 20 mm was counted, and the peeling rate shown by the following formula was used for evaluation. Peeling rate of alloy layer = (100 × peeling length of alloy layer <mm> total) / 20 <mm>

The alloy peeling rate is qualified as less than 15%. (7) ZnO disappearance test

The steel sheet of each test example was punched into 30 mmφ, and was superposed on a SiC furnace base of 70 mm × 70 mm, and a SUS304 steel block of 50 mm × 50 mm × 70 mm heated at 900 ° C. was placed in a state of It was heated in a furnace at 900 ° C. for 6 minutes, and immediately after being taken out, it was clamped in a stainless steel mold for rapid cooling. The amount of Zn deposited before and after heating was measured by XRF to measure the amount of Zn deposited in Zn conversion, and the ZnO residual ratio was calculated.

In the evaluations shown in Table 4, a pass rate of 75% or more based on the Zn residual rate was acceptable, and a pass rate of 0.40 g / m ² or more based on the Zn residual rate was acceptable. (8) Point welding

The spot weldability was evaluated as follows.

Each of the produced steel plates of the test examples was put into a heating furnace and heated in a furnace at 900 ° C. for 6 minutes, and immediately after being taken out, it was clamped in a stainless steel mold for rapid cooling. The cooling rate at this time was about 150 ° C / second. Next, each steel sheet after cooling was cut into 30 × 50 mm, and the appropriate current range (upper limit current-lower limit current) for point welding was measured. The measurement conditions are shown below. The lower limit current is set to a current value when the nugget diameter becomes 3 × (t) ^0.5 , and the upper limit current is set to a current at which a splash occurs. Current: DC electrode: chrome-copper, DR (front end 6mmφ is 40R) pressure: 400kgf (1kgf is 9.8N) energizing time: 240 ms

The larger the value is, the better the spot weldability is. In the evaluation shown in Table 4, a pass of 1.0 kA or more is considered acceptable. (9) Corrosion resistance after coating after hot working

After inserting 200 mm × 200 mm steel plates of each test example into the furnace, and setting the evaluation surface so as not to contact the pedestal of the SiC furnace, it was heated at 900 ° C for 6 minutes and then taken out of the furnace. Clamped in a stainless steel mold (50mm punch diameter, shoulder R3mm, pressure of 500kg), cup-shaped processing to a depth of 50mm, and then quenched. The flange portion cooling rate at this time was about 150 ° C / second. Next, each of the cooled cup-shaped steel plates was subjected to chemical conversion treatment with a chemical conversion treatment liquid (PB-SX35) manufactured by Japan Pakase Seiki Co., Ltd., and then coated with electricity manufactured by Japan Paint Co., Ltd. The coating material (Powernics 110) was deposited to a thickness of 20 μm, and was fired at 170 ° C. In addition, each steel plate of 70 mm × 150 mm to which a thermocouple was fused was inserted into an atmospheric furnace set at 900 ° C., and the temperature until the temperature became 900 ° C. was measured, and the average temperature rise rate was calculated to be 5 ° C./second.

The post-painting corrosion resistance evaluation is performed by the method prescribed by JASO M609 formulated by the Automobile Technology Association. That is, the coating film was cross-cut with an acrylic cutter in advance, and the swelling width (unilateral maximum value) of the coating film from the cross-cut after 180 cycles (60 days) of the corrosion test was measured.

The corrosion resistance after coating after hot working is less than 7mm.

The above results are shown in Table 2. [Table 2]

The results are shown in Table 2. It is clear from Table 2 that in the sample numbers 14 to 25 and 31, the average amount of Si contained in the Al-based plating layer 103 is 6% or more and the alloy layer thickness is reduced. As a result, the alloy layer peeling rate is less than 15% The processability is good. In addition, it can be seen that the Si area ratio on the surface of the Al-based plating layer 103 is 12% or less, the plating adhesion amount is 30 g / m ² or more, and the maximum value of the Si concentration distribution in the thickness direction of the Al-based plating layer is expressed as mass%. 15% or less, and the ratio of the maximum value of the Si concentration in the thickness direction to the minimum value of the Fe concentration in the region of 4% by mass or less in the plating is 1.0 or more and 2.0 or less, so the corrosion resistance after coating after hot working Will be less than 7mm, and good results are obtained.

In addition, ZnO did not disappear after hot pressing, and the weldability was also excellent.

On the other hand, in sample numbers 1 to 3, the average amount of Si contained in the Al-based plating layer 103 was less than 6%, which resulted in a thicker alloy layer. As a result, the peeling rate of the alloy layer was greater than 15% and the workability was poor. In addition, it can be seen that the sample numbers 4 to 13 do not give good results in terms of corrosion resistance after coating after hot working because the area ratio of Si on the surface of the Al-based plating layer 103 is greater than 12%. Sample Nos. 26 and 27 were subjected to water mist cooling, which caused the surface roughness to become too large, and the corrosion resistance after coating was deteriorated.

Sample Nos. 28, 29, and 30, because the plating layer was removed by pickling, rust was formed during heating, and the weldability and corrosion resistance after coating deteriorated.

The maximum value of the Si concentration distribution in the thickness direction of Sample No. 32 was too large, and the corrosion resistance after coating was unsatisfactory.

In addition, for sample numbers 4 to 13, 26, 27, 33, and 34, the ratio of the maximum value of the Si concentration in the thickness direction to the minimum value of the Fe concentration in the region of 4% by mass or less in the plating is greater than 2.0, so it is hot. After pressing, a second layer is formed during hot pressing, which deteriorates the corrosion resistance after coating.

In Examples 1 to 3, although the ratio of the maximum value of the Si concentration in the thickness direction to the minimum value in the region where the Fe concentration was 4% by mass or less was greater than 2.0, the average Si concentration in the plating was low. Therefore, the second phase is not formed. However, the alloy layer was peeled.

100‧‧‧Al series plated steel plate

101‧‧‧ mother material

103‧‧‧Al-based plating

107‧‧‧ surface coating

109‧‧‧ZnO particles

111‧‧‧Organic resin

Figure 1 shows the relationship between the Si concentration in the Si-containing Al-based plating bath and the surface Si area ratio.

Fig. 2 is a microscope photograph of a cross section of an Al-based plating layer after being heated at 950 ° C for 0.5 minutes.

FIG. 3 is a concentration distribution map in the depth direction of FIG. 2 for Al, Si, and Fe, and the values from 1 to 5 indicate the areas corresponding to the areas with the same numbers in FIG. 2.

4 is a schematic cross-sectional view of an Al-based plated steel sheet of the present invention in which an Al-based plated layer is provided on the surface of a base material.

5 is a schematic cross-sectional view of an Al-based plated steel sheet of the present invention provided with an Al-based plated layer and a surface coating layer.

FIG. 6 is a graph showing the Si concentration distribution in the thickness direction of the plating layer.

FIG. 7 is a diagram showing the Si concentration distribution in the thickness direction of the plating layer.

FIG. 8 is a graph showing the Si concentration distribution in the thickness direction of the plating layer.

Claims (5)

An Al-based plated steel sheet characterized in that the average composition of Al contained in the Al-based plating layer is 85% or more by mass%, and the Si in the Al-based plating layer is 4% or more by mass% and 12% or less, plating adhesion amount is 30g / m ² or more, Si area ratio of plating surface is 12% or less, and maximum value of Si concentration distribution in thickness direction of Al-based plating layer is 15% or less in mass% The ratio of the maximum value of the Si concentration distribution in the thickness direction of the Al-based plating layer to the minimum value of the Si concentration when the Fe concentration is 4% by mass or less is 1.0 or more and 2.0 or less. The Al-based plated steel sheet according to claim 1, wherein the surface roughness of the aforementioned Al-based plated layer is 0.1 μm or less based on the arithmetic average roughness Ra. For example, the ratio of the maximum value of the Si concentration distribution in the thickness direction of the aforementioned Al-based plating layer to the minimum value of the Si concentration when the Fe concentration is 4% by mass or less is the Al-based plated steel sheet of claim 1 or claim 2 as 1.0 ~ 1.5. For example, the Al-based plated steel sheet according to claim 1 or claim 2 includes a surface coating layer which is provided on the Al-based plating layer and contains ZnO particles and an organic resin. adhesion amount of Zn metal in terms of 0.5g / m ² or more and ² or less at 10.0g / m. A method for manufacturing an Al-based plated steel sheet, which is characterized in that the following steps are performed: a plating step in which a steel sheet is immersed in an Al plating bath containing Si in an amount of 6% to 15% by mass to form a plating Cooling step, cooling the steel sheet after immersion; etching step, immersing the cooled steel sheet in an acidic solution below pH 1 and etching the surface layer to the following depth: the Si area ratio of the plating surface is 12% or less, The maximum value of the Si concentration distribution in the thickness direction of the Al-based plating layer is 15% or less in terms of mass%, and the maximum value of the Si concentration distribution in the thickness direction of the Al-based plating layer and the Fe concentration are 4% by mass or less. The ratio of the minimum value of the Si concentration is 1.0 or more and 2.0 or less.