TW202003132A - Al-based plated steel sheet and manufacturing method therefor is capable of sufficiently exhibiting corrosion resistance after painting and is suitable for hot pressing - Google Patents

Abstract

An Al-based plated steel sheet is characterized in that the average composition of Al contained in the Al-based plating layer is at least 85% in mass%, Si contained being at least 4% and at most 12% in mass%, a coating amount being at least 30 g/m2e, the Si area ratio of the plating surface being at most 12%, a maximum value of the Si concentration distribution in a thickness direction of the Al plating layer being at most 15% in mass%, a ratio of the maximum value of the Si concentration distribution in the thickness direction of the thick Al-based plating layer to a minimum value of the Si concentration for Fe concentration being at most 4% in mass being at least 1.0 and at most 2.0.

Description

Al series plated steel plate and manufacturing method thereof

The present invention relates to an Al-based plated steel sheet that can fully exhibit corrosion resistance after coating in terms of hot pressing and its manufacturing method.

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 mobile means for daily life, also seeks to use the weight reduction of the car body to suppress fuel consumption without exception. There are many automobile parts 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 plate alone, and it is also required to maintain the mechanical strength of the steel plate. As mentioned above, the demand for steel plates is gradually increasing not only in the automotive industry, but also in various manufacturing industries. Therefore, by improving the mechanical strength of steel plates, research and development have been conducted on steel plates that can maintain or improve the mechanical strength even if the steel plates used in the past are thinned.

In general, a material having excellent mechanical strength tends to have reduced formability and shape freezeability in forming processes such as bending, and when processing into complex shapes, the process itself is difficult. As one of the means to solve this formability problem, the so-called "hot pressing method (also called hot stamping method, hot pressing method, die quenching method, pressure hardening)" can be cited. This hot pressing method is to heat the material to be formed to a high temperature (Wostian iron zone), and then press the steel plate softened by heating to form it and then cool it.

According to the 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 of cooling after forming can be used to improve the mechanical strength of the material. Therefore, by using this hot pressing, a molded product having both good shape freezeability and high mechanical strength can be obtained.

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

An example of suppressing such a decrease in productivity is a method of forming a film on a steel sheet. In general, various materials such as organic materials and inorganic materials are used for the coating on the steel plate. Among them, zinc-based plated steel sheets that have a sacrificial anticorrosive effect on steel sheets are widely used in automotive steel sheets and the like based on their own anticorrosion performance and steel sheet production technology.

However, the heating temperature (700°C or more and 1000°C or less) of hot pressing is higher than the decomposition temperature of organic materials 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 will evaporate, and the surface properties may be significantly deteriorated.

Therefore, at the time of hot pressing, it is preferable to form, for example, 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 make a so-called Al-based plated steel plate. By forming an Al-based metal film, it is possible to prevent the rust from adhering to the surface of the steel plate without requiring steps such as a rust removal step, so productivity is improved. In addition, the Al-based metal film also has an anti-rust effect, so the corrosion resistance after painting will also be improved.

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

As one of the means to solve the above-mentioned problems, a method of attaching a coating layer containing zinc oxide (ZnO) to the plated surface has been proposed (see, for example, Document 1 (International Publication No. 2013/157522), Document 2 (International Publication No. 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 coating layer containing a resin component or a silane coupling agent as a binder to the surface of a steel sheet in order to suppress the shedding of ZnO, and applying the binder during hot pressing The organic solvent component volatilized and only ZnO remained. With the above method, the voids generated by the burning and evaporation of the organic solvent make ZnO and the mold metal come into point contact, and the lubricity is improved.

By forming a surface coating layer containing ZnO on the Al-based plating layer, the slidability during hot pressing is improved. However, recently, due to the complexity of the pressed shape, the Al-based plating layer is easily peeled off during processing. In addition, in order to increase 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 plating, the formation of an alloy layer of steel and Al may be a problem, and in order to suppress the growth of the alloy layer, Si is added to the plating bath. In normal molten Al-based plating, it is cooled at 10°C/sec after being pulled up from the plating bath. At this time, the surface layer of the plating is non-equilibrium solidification and is covered with eutectic with concentrated Si.

SUMMARY OF THE INVENTION The present invention was made in view of the above circumstances, and an object thereof is to provide an Al-based plated steel sheet for hot pressing that can fully exhibit corrosion resistance after coating and a method for manufacturing the same.

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

In general, if Si is contained in the Al-based plating layer, in the plating step for manufacturing the Al-based plating steel sheet, the plating-based Al solidifies from the steel sheet side as the primary crystals. Therefore, on the surface of the Al-based plating layer, Si will be concentrated to a high concentration on the surface side of the final solidification. Figure 1 shows that after the Al-based plating containing Si is applied to the steel plate by a general method, the EPMA (measurement equipment is JXA8500F manufactured by Nippon Electronics Co., Ltd.). The distribution pattern is 500 points × 500 points, and the step interval is 1 μm, beam diameter 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 of the surface of the Al-based plating layer. It is clear from FIG. 1 that the Si area ratio on the surface is about 3 times thicker than the Si concentration of the entire Al-based plating layer.

If heating conditions for hot-pressing the Al-based plated steel sheet containing Si in the Al-based plated layer as described above (furnace temperature 900°C or higher and 950°C or lower × residence time in the furnace 0.5 minutes or longer and 6 minutes or shorter) To heat, as shown in Figures 2 and 3, there will be 5 layers with different concentrations of Al, Si and Fe. The outermost layer, that is, the first layer is an AlFe layer with a low Si concentration, and the second layer below it (the second layer from the surface in five layers) becomes a layer with a high Si concentration. This high Si layer (second layer) shows the highest potential in the five layers and promotes the cathodic reaction of corrosion (reduction reaction of dissolved oxygen). Therefore, if the second layer is exposed, there is a tendency to promote corrosion.

That is, it was found that if the Si area ratio of the plated surface becomes higher in the plating stage before the hot press heating, it becomes easier to generate the second layer with a high Si concentration in the heating stage of the hot press. 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 the Al-based plated steel sheet, the Al-based plating starts to solidify from the steel sheet side, and Si will be concentrated to a high concentration on the surface side that is finally solidified. It can be seen that this phenomenon increases the Si area ratio in the plated surface.

In addition, it can also be seen that even when Si is not concentrated on the surface but concentrated inside, the second layer is formed during hot pressing.

The inventors have found out that by removing the Si-concentrated portion after the plating and solidification by pickling, the workability and the corrosion resistance after painting at the time of 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 plated layer is 85% or more in mass %, and Si is 4% or more and 12% or less in mass% , The plating adhesion amount is 30 g/m ² or more, 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 in 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 Al-based plated layer is 0.1 μm or less in terms of arithmetic average roughness Ra.

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

[4]. The Al-based plated steel sheet according to any one of [1] to [3], which has 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 sheet, characterized in that the following steps are performed: a plating step in which the steel sheet is immersed in an Al plating bath containing 6% or more and 15% or less of Si by mass, To form a plating layer; a cooling step to cool the aforementioned steel sheet after immersion; an etching step to immerse the aforementioned cooled steel sheet in an acidic solution having a pH below 1 and etch the surface layer to the following depth: Si area ratio of the plating surface 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 mass %, and the maximum value of the Si concentration distribution and the Fe concentration in the thickness direction of the Al-based plating layer 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, an object is to provide an Al-based plated steel sheet for hot pressing that can fully exhibit corrosion resistance after painting and a method for manufacturing the same.

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

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 formed by forming an Al-based plated layer 103 on the surface of the 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 joined by an organic resin 111. Each layer will be described in detail below. However, FIGS. 4 and 5 are examples in which the Al-based plating layer 103 and the 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 plated layer 103) used for the Al-based plated steel sheet 100 of this embodiment is used to have excellent mechanical strength even after hot pressing after forming the plated layer (meaning Refers to the tensile strength, yield point, elongation, depth ratio, hardness, impact value, fatigue strength, creep strength and other mechanical deformation and destruction properties). For example, a member whose quenchability is improved by adding C (carbon) or an alloy element is used. With this, the automotive parts obtained by applying hot pressing to the Al-based plated steel sheet 100 formed by forming the Al-based plated layer 103 and the surface coating layer 107 described later can exhibit excellent mechanical strength.

That is, as the base material 101 for the Al-based plated steel sheet 100 of the present embodiment, as long as it has excellent mechanical strength, well-known materials can be used. For example, a material having the following composition can be used as the base material 101, but the composition of the base material 101 is not limited to this.

The base material 101 of this embodiment contains, for example, 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 in mass %. , Al: 0.001% or more and 0.1% or less, N: 0.01% or less, and can optionally contain 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% 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, may further contain W, V, Nb , Sb and other elements, and the remaining part is composed of Fe and unavoidable impurities. The components added to the base material 101 will be described in detail below. 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 it is contained in order 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 better 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 alloying 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 greater than 0.5%, the base material 101 can be more hardened, but it will easily melt fracture. Therefore, the content of C is preferably 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 the content of 0.1% or more and 0.4% or less. Also, the C content is more preferably 0.15% or more and 0.35% or less. (Si: 2.0% or less)

Silicon (Si) is added as a deoxidizer and other elements that cannot be avoided during steel refining. However, excessive addition of Si will cause a reduction in ductility in the hot rolling step during the production of the steel sheet, or damage the surface properties as a result, so it is preferably set to 2.0% or less.

In addition, Si is one of the strengthening elements that can increase the mechanical strength of the base material 101, and it can also 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 improving 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, if the Si content is more than 0.6%, the wettability will decrease when molten Al-based plating is performed, and unplated may occur. Therefore, Si is preferably added in a content of 0.01% or more and 0.6% or less. In addition, the Si content is more preferably 0.05% or more and 0.5% or less. (Mn: 0.01% or more and 3.5% or less)

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

In addition, Mn is one of the strengthening elements of the base material 101 and one of the elements that can improve the hardenability. In addition, Mn is also effective in suppressing low thermal embrittlement 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 exceeds 3%, the residual γ phase may become excessive and the strength may decrease. Therefore, Mn is preferably added in a content of 0.5% or more and 3% or less. Moreover, the Mn content is more preferably 1% or more and 2% or less. (P: below 0.1%)

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

The sulfur (S) system cannot avoid the elements it will contain, and it will become inclusions in the base material 101 as MnS and become the starting point of destruction, which will hinder the ductility or toughness and cause the deterioration of workability. Therefore, the lower the S content, the better. 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 is preferably 0.001%. Furthermore, the S content is more preferably 0.01% or more and 0.02% or less. (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 Al content should be set to 0.1%. On the other hand, the lower limit of the Al content is not particularly defined, but it is preferably set to, for example, 0.001% based on the economical refining limit. Moreover, the Al content is more preferably 0.01% or more and 0.08% or less. (N: below 0.01%)

Nitrogen (N) is an element that cannot be avoided. From the viewpoint of stabilizing various characteristics of the base material 101, its content is preferably fixed, and specifically, it can be fixed according to the content of elements such as Ti and Al. On the other hand, if the N content is too large, the content of Ti, Al, etc. will increase, so that the manufacturing cost of the base material 101 can be expected to increase, so the upper limit of the N content is preferably 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: one or more of 0.005% or more and 1.0% or less) (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 also 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, for example, carbide or nitride is formed, and the base material 101 may be softened. In particular, if the Ti content is greater than 0.1%, there is a high possibility that the intended mechanical strength cannot be obtained. Therefore, Ti is preferably added in a content of 0.005% or more and 0.1% or less. Moreover, 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 to increase the strength of the base material 101 during quenching.

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

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

Nickel (Ni) has the effect of improving the hardenability during hot pressing. Furthermore, Ni also 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 exceeds 5.0%, not only will the above effects be saturated, but also the manufacturing cost of the steel sheet will increase. Therefore, Ni is preferably added in a content of 0.01% or more and 5.0% or less. (Mo: 0.005% or more and 2.0% or less)

Molybdenum (Mo) has the effect of enhancing the hardenability during hot pressing. Moreover, Mo also has an 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 exceeds 2.0%, not only will the above effects be saturated, but also the manufacturing cost of the steel sheet will increase. Therefore, Mo should be added at a content of 0.005% or more and 2.0% or less. (Cu: 0.005% or more and 1.0% or less)

Copper (Cu) has the effect of enhancing the hardenability during hot pressing. Moreover, 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 exceeds 1.0%, not only will the above effects be saturated, but also the manufacturing cost of the steel sheet will increase. Therefore, Cu is preferably added in a content of 0.005% or more and 1.0% or less. (W, V, Nb, Sb)

In addition to the above-mentioned plurality of elements, the base material 101 of this embodiment may optionally add elements such as tungsten (W), vanadium (V), niobium (Nb), and antimony (Sb). As long as the addition amount of these elements is in a well-known range, any addition amount can be adopted. (The remaining part)

The remaining part of the base material 101 is only iron (Fe) and unavoidable impurities. The so-called unavoidable impurities refer to components contained in the raw materials or components mixed in the manufacturing process, and refer to components that are not 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 plate with excellent mechanical strength like this, if it is processed by hot pressing, it can be pressed in a state softened by heating, so it can be easily formed. Moreover, after pressing, the base material 101 cooled from a high temperature can achieve high mechanical strength, and even if the thickness is thinned 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, the Si-based plating element is added as an element that suppresses the formation of the Fe-Al alloy layer during hot plating. If the Si content in the Al-based plating layer 103 is less than 4% by mass, the Fe-Al alloy layer will grow excessively during the hot-dip plating, and therefore the plating layer will be broken during the pressing process. On the other hand, when the Si content is greater 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 will still be 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. In addition, 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. Components other than Al and Si are not particularly limited, but Zn evaporates due to heating before hot pressing, so it is preferably 10% by mass or less or should not be contained in an amount greater than the unavoidable amount of impurities. In addition, Fe also contains Fe due to alloying with Fe in the base material. In addition, it is preferably an Al-Si alloy such as JIS 4000 series aluminum alloys other than Al and Si, which are unavoidable impurities (Al alloys composed of Al and Si, and are unavoidable impurities other than Al and Si Of aluminum alloy).

The Si content 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 rust (iron oxide) 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 rust removal step, the surface purification step, and the surface treatment step can be omitted, thereby further improving the productivity of automobile parts and the like. In addition, the Al-based plating layer 103 has a higher melting point than the coatings of organic materials or other metal-based materials (for example, Zn-based materials), so it can be processed at high temperatures 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 by the components in the Al-based plating layer and disappearing during hot pressing.

In addition, a part of Al contained in the Al-based plating layer 103 may be alloyed with Fe in the base material 101 at the time of molten plating or hot pressing. Therefore, the Al-based plating layer 103 is not necessarily formed as a single layer with a fixed composition, and may also be a layer containing a partially alloyed layer (alloy layer) or a steel-aluminum inclined alloy layer whose concentration gradient changes from the surface Things. (Amount of plating adhesion)

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 plating thickness becomes too thin, so that rust will be generated during hot pressing and the corrosion resistance will deteriorate. It is preferably 50 g/m ² or more. (Si area ratio of Al-based plating layer 103 surface)

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

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

Therefore, the area ratio of Si 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%, 1% on the practical surface is a substantial lower limit.

The area ratio of Si on the surface of the Al-based plating layer 103 can be determined by EPMA (Electron Probe Micro Analyzer) area analysis or Auger Electron Spectroscopy (AES) area analysis after plating. At this time, if it is EPMA, JXA8500F manufactured by JEOL is used as the measuring device, and the measuring point is 500 points × 500 points, with a pitch of 1 μm and a beam diameter of 1 μm. In practice, it is desirable to perform measurement in a field of view of 5 mm×5 mm with a beam diameter of 10 μm or less, a measurement point of 500 points×500 points, and a pitch of 10 μm. In addition, the Si area ratio can also be obtained 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 area ratio of Si on the surface of the Al-based plating layer 103 is to be measured later, quantitative analysis of the depth direction from the surface can also be performed by high-frequency glow discharge spectrometry (high-frequency GDS) , And set as follows to obtain.

In the high-frequency glow discharge spectrometry (high-frequency GDS), it is advisable to measure the range of 4 mm in diameter. With high-frequency GDS, the part other than the Al and Si of the plating component is defined as the elemental surface of 5% by weight, and after the concentration (atomic %) of each component in the part is determined, the component The specific gravity and atomic weight (molecular weight) 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 determined 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 and Si is concentrated, the Si concentrated eutectic on the surface is dissolved in an acidic solution below pH 1 to reduce the surface area ratio of Si to 10% about. Furthermore, when the cooling rate at the time of solidification is 20°C/sec, the Si concentration of the eutectic 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 the 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 in mass% (preferably 12% by mass or less), 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. The reason for the foregoing is as follows.

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

On the other hand, even if there is a portion with a high Si concentration not in the surface layer as shown in the upper part of FIG. 7, this part will be easily generated as shown in the lower part of FIG. 7 during the heating stage of hot pressing as shown in the lower part of FIG. 7 Layer 2.

Therefore, as shown in the middle part of FIG. 8, even if it is not the surface but the inside, there can be no part with a high Si concentration.

This is the reason for specifying the Si concentration distribution in the thickness direction. In addition, the reason for using the Si concentration when the Fe concentration is 4% by mass or less as the minimum value is due to the fact that the interface between the plating layer and the base material is alloyed.

Ideally, the ratio of the maximum value of the Si concentration distribution in the 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 performing composition analysis of the vertical cross section of the Al-plated steel sheet using EPMA or the like.

The method of obtaining such a concentration distribution can be exemplified by the method of etching the surface. For example, if the Si in the plating layer shows a plated steel sheet with the concentration distribution shown in the upper part of FIG. 8, as long as the plating layer is removed by etching to the 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 of 8. With this concentration distribution, after hot pressing, as shown in the lower part of FIG. 8, a second layer with a high Si concentration will not be formed in the plating layer.

The etchant is not particularly limited as long as it is an acidic solution having an iron-based inhibitor at a pH of 1 or lower, and an H ₂ SO ₄ aqueous solution containing an iron-based inhibitor at a concentration of 2 mol% or more can be exemplified. If it is an acidic solution greater than pH 1, the etching may not proceed, or even if it proceeds, the etching rate may be too slow and productivity may deteriorate.

The following methods can be exemplified: dipping in an alkaline solution of sodium hydroxide aqueous solution with a concentration of 2 mol% or more in other etching solutions, dissolving the plated metals Al and Si, and then dissolving the remaining Al-Si with the above acidic solution -Fe alloy layer.

The etching time is a time period in which a portion with a high Si concentration can be removed and the amount of adhesion of plating becomes 30 g/m ² or more. Specifically, the etching is performed up to the following depth: 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 in 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 of the immersion liquid or the concentration of sulfuric acid, the immersion treatment time can be shortened. And can also grind the plating surface to remove the Si concentration layer on the surface.

In order not to form a portion with a high Si concentration in the Al-based plating layer 103, there is also a method of setting the cooling condition after immersion in the plating bath 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 arithmetic average roughness Ra. When it is larger than 0.1 μm, the surface unevenness will become too large and a locally thin region may be generated, and there is a risk of rust formation during hot pressing. In addition, when the surface coating layer 107 is provided, a locally thin region may be generated, so that the effect as the surface coating layer 107 cannot be sufficiently obtained.

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

In order to further improve the thermal lubricity during hot pressing, a surface coating 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 having an average particle diameter of 0.10 μm or more and 5.00 μm or less, and an organic resin 111, and the adhesion amount of the ZnO particles 109 is preferably 0.5 g/m ² or more and 10.0 in terms of metal Zn. g/m ² or less. In addition, when Al-based plating layers 103 are formed on both surfaces of the base material 101, a surface coating layer 107 can be formed on at least one side of the plating layer.

The surface coating 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, ZnO particles 109 having an average particle diameter of 0.10 μm or more and 5.00 μm or less are preferably converted into 0.5 g/m ² and 10.0 g in terms of metal Zn. /m ² or less. The ZnO particles 109 will be in point contact with the mold, resulting in a reduction in the dynamic friction coefficient and improved 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 the pressing process, and the thermal lubricity will not be sufficiently improved.

On the other hand, if the average particle diameter of the ZnO particles 109 is greater than 5.00 μm, the weldability deteriorates. Although ZnO is insulative, when the particle size is small, it will be crushed during welding and pressurization, and the conduction point can be sufficiently ensured. However, if the average particle size of the ZnO particles 109 becomes larger and larger than 5 μm, the ZnO particles 109 will not be easily crushed during welding and pressurization. As a result, the energization point cannot be sufficiently secured and dust is likely to be generated, so the weldability deteriorates.

The method for measuring the average particle diameter of ZnO particles 109 is not particularly limited. For example, an arbitrary number of 10 or more ZnO particles 109 may be observed at 2000 times using a scanning electron microscope (SEM, Scanning Electron Microscope), etc., and the maximum particle diameter of each particle may be measured, and then the average value may be calculated and obtained. Alternatively, the average particle diameter of the ZnO particles 109 may be determined using a particle size distribution measuring device.

Moreover, if the amount of all ZnO particles 109 attached to 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.

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

In addition, the amount of adhesion here refers to the amount of adhesion before being placed on the conveyor belt and heated during hot pressing. (Organic resin 111)

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

In order to allow the organic resin 111 to fully exhibit its role as a binder, the content of the organic resin 111 relative to the entire surface coating layer 107 is preferably 10% or more and 60% or less in terms of mass %. If the above content is less than 10%, the effect as a binder cannot be fully exhibited, so that the coating film before heating becomes easily peeled off. In addition, in order to stably obtain the function as a binder, it is more preferable to provide the above content of the organic resin 111 to be 15% or more. On the other hand, if the content of the organic resin 111 is greater than 60%, an unpleasant odor will become apparent when heated.

The method of forming the surface coating layer 107 on the Al-based plating layer 103 is not particularly limited. The surface coating layer 107 can be formed by applying an aqueous solution or a solvent obtained by dissolving the above-mentioned main components on the Al-based plating layer 103 by a well-known technique 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 energized heating can be used. In addition, for the temperature increase temperature during drying, it is preferable to appropriately set the glass transition temperature (Tg) of the organic resin 111 which is a binder. <Manufacturing method>

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

First, the steel plate is immersed in an Al plating bath containing 6% or more and 15% or less of Si 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 aforementioned steel sheet after immersion is cooled (cooling step). The cooling should be air-cooled. This is because if it is cooled by water mist, the surface roughness becomes too large, and the amount of plating to be removed during etching increases. The cooling rate is not particularly limited, but preferably 5 to 15°C/sec.

Next, the cooled steel sheet is immersed in an acidic solution having a pH of 1 or less, and the surface layer is etched to the following depth: the area ratio of Si on the plated surface is 12% or less, and the Si concentration distribution in the thickness direction of the Al-based plated layer The maximum value in 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 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 plate) of the present invention, the Si area ratio of the surface of the Al-based plated layer 103 can be suppressed, thereby suppressing the generation of high Si concentration in the heating stage of hot pressing 2 layers to prevent deterioration of corrosion resistance after painting after hot working. Moreover, according to the Al-based plated steel sheet 100 of this embodiment with the surface coating layer 107 added, the presence of the surface coating layer 107 having excellent lubricity can suppress the adhesion to the mold. Even if the Al-based plating layer 103 is pulverized by heating, the presence of the surface coating layer 107 with excellent lubricity can still suppress the adhesion of the powder (Al-Fe powder, etc.) to the mold used for subsequent pressing. Therefore, when the steel sheet of the present embodiment is hot-pressed, there is no need to remove the Al-Fe powder adhered to the mold, etc., and excellent productivity can be achieved.

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

Using a cold-rolled steel sheet (plate thickness 1.4 mm) of the chemical composition shown in Table 1 (the balance is Fe and unavoidable impurities), an Al-based plating layer 103 was formed on both sides by the Sendzimir 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% or more and 19% or less in mass %, and further contains Fe eluted from the base material 101. After dissolving the Al-based plating layer 103 with an aqueous solution of hydrochloric acid added with an inhibitor, the amount of Si in the Al-based plating layer 103 in the solution was measured by high-frequency inductively coupled plasma luminescence spectrometry (ICP), and it was confirmed that It is the amount described in Table 2. [Table 1]

The amount of adhesion of the Al-based plating layer 103 to the base material 101 was adjusted to 160 g/m ^{2 on} one side by the 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, sample numbers 19 and 23 It was implemented at 22°C/sec. Sample Nos. 1 to 13 are those after the formation of the Al-based plating layer 103, and the dissolution treatment by pickling after plating solidification is not performed. On the other hand, for sample numbers 14 to 25, after cooling the base material 101 on which the Al-based plating layer 103 is formed, it was immersed in a 10% sulfuric acid solution for 30 seconds, and the sample number 28 was immersed for 300 seconds. Sample No. 29 was immersed for 250 seconds, Sample No. 30 was immersed for 200 seconds, Sample No. 31 was immersed for 150 seconds, Sample No. 32 was immersed for 15 seconds, and Sample No. 33 was immersed for 5 seconds.

Sample No. 26 was set to water mist cooling, and TiO particle suspension was used to accelerate the solidification rate by the solidification nucleation of the particles and the rapid cooling with the aqueous solution to promote solidification.

Sample No. 27 was also set to water mist cooling, and a VO particle suspension was used. The solidification rate was accelerated by the solidification nucleation of the particles and the rapid cooling with an aqueous solution, thereby promoting solidification.

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

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

After that, the surface coating layer 107 is formed. When the surface coating layer 107 is to be formed, a solution is obtained by mixing and adjusting ZnO particles 109 and organic resin 111 in a solvent, and this solution is applied to the Al-based plating layer 103 and applied 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 plates of the test examples prepared 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 the three measurement points was used as the plating thickness. (2) Plating adhesion

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

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

After immersing the steel plates of each test example cut into a width of 50 mm × a length of 50 mm in a 10% sulfuric acid aqueous solution prepared by adding 0.5% by mass of an inhibitor (HIBIRON Y-30 manufactured by Sugimura Chemical Industry Co., Ltd.) to dissolve the plating, use ICP The dissolved solution was quantitatively analyzed, and the Si concentration was measured by a calibration curve method.

In the high-frequency GDS, the depth direction distribution of Si intensity converted into Si concentration is taken, and the maximum value is the maximum value of the Si concentration distribution in the thickness direction of the plating, and the minimum value in the area where the Fe concentration is 4 mass% or less The value is the minimum value of the Si concentration distribution in plating. The ratio of the maximum value to the minimum value is the maximum value/minimum value. (5) Alloy layer thickness

After embedding the steel plates of each test example cut into a width of 10 mm and a length of 30 mm into the resin, the cross section was polished and the vertical cross section in the longitudinal direction was observed. After selecting any 20 points from the 20 mm width and measuring the thickness of the alloy layer, the average of the 20 points is taken as the thickness of the alloy layer. (6) Peeling rate of alloy layer

In the tensile test, the steel plates of each test example having a width of 30 mm and a length of 300 mm were processed to have an elongation of 10% in the L direction. Then, the sample was cut out from the center in the L direction to have a width of 10 mm and a length of 30 mm and was embedded in the resin, followed by grinding. Section and observe the vertical section in the L direction. The width of the peeling part of the alloy layer scattered in the width of 20 mm was counted, and the peeling rate shown by the following formula was evaluated. Peeling rate of alloy layer = (100 × peeling length of alloy layer <mm> total)/20 <mm>

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

After punching the steel plates of each test example to 30 mmφ, they were superimposed on a pedestal made of SiC furnace of 70 mm×70 mm, and placed on a SUS304 steel block of 50 mm×50 mm×70 mm heated at 900° C. with It was heated in an oven at 900°C for 6 minutes, and was immediately clamped in a stainless steel mold for rapid cooling after being taken out. The amount of Zn adhesion before and after heating was measured by XRF to measure the Zn conversion Zn adhesion amount, and the Zn conversion ZnO residual rate was calculated.

In the evaluation shown in Table 4, the residual Zn rate was 75% or more as the pass, and the residual Zn amount was 0.40 g/m ² or more as the pass. (8) Point weldability

The point weldability is evaluated as follows.

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

The larger the above value means the better the spot weldability, and in the evaluation shown in Table 4, 1.0 kA or more was considered as a pass. (9) Corrosion resistance after painting after hot processing

After inserting 200mm×200mm steel plates of each test example into the furnace and setting it so that the evaluation surface does not contact the SiC-made furnace pedestal, heat the furnace at 900°C for 6 minutes and take it out of the furnace immediately. It is sandwiched between stainless steel molds (punch diameter 50mm, shoulder R3mm, pressing pressure 500kg), and cup-shaped processing is performed to a depth of 50mm, and then quenched. At this time, the cooling rate of the flange portion is about 150°C/sec. Next, each cup-shaped steel plate after cooling was subjected to chemical conversion treatment with a chemical conversion treatment liquid (PB-SX35) manufactured by Japan Pakase Seiki Co., Ltd., and then painted by Japan Paint Co., Ltd. A paint (Powernics 110) was deposited to make the film thickness 20 μm, and baked 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., the temperature was measured until it reached 900° C., and the average heating rate was calculated to be 5° C./sec.

The corrosion resistance evaluation after painting is carried out by the method specified in JASO M609 developed by the Automotive Technology Association. That is, the coating film was cross-cut with an acrylic cutter in advance, and the swelling width (maximum value of one side) of the coating film from the cross-cut after 180 cycles (60 days) of the corrosion test was measured.

After hot working, the corrosion resistance after painting is qualified as less than 7mm.

Table 2 shows the above results. [Table 2]

The results are shown in Table 2. As is clear from Table 2, 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 thickness of the alloy layer becomes thin. As a result, the peeling rate of the alloy layer is less than 15% And the processability is good. In addition, it can be seen that the area ratio of Si on the surface of the Al-based plating layer 103 is 12% or less, the amount of plating adhesion 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 in mass% 15% or less, and the ratio of the maximum value of the Si concentration in the thickness direction of the plating to the minimum value of the area where the Fe concentration is 4% by mass or less is 1.0 or more and 2.0 or less, so the corrosion resistance after coating after hot working It will be less than 7mm with good results.

In addition, ZnO does not disappear after hot pressing, and the weldability is also excellent.

In contrast, in sample numbers 1 to 3, the average value of the amount of Si contained in the Al-based plating layer 103 was less than 6%, which caused the thickness of the alloy layer to increase. As a result, the peeling rate of the alloy layer was greater than 15% and the workability was poor. In addition, it is understood that in Sample Nos. 4 to 13, since the area ratio of Si on the surface of the Al-based plating layer 103 is greater than 12%, good results have not been obtained in terms of corrosion resistance after coating after hot working. Sample Nos. 26 and 27 were subjected to water mist cooling, which resulted in an excessively large surface roughness and deteriorated corrosion resistance after painting.

In sample numbers 28, 29, and 30, the plating layer was removed by pickling, so rust was formed during heating, and the weldability and corrosion resistance after painting deteriorated.

The maximum value of the Si concentration distribution in the thickness direction of sample No. 32 is too large, but the corrosion resistance after coating is unacceptable.

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 area where the Fe concentration is 4 mass% or less in the plating is greater than 2.0, so the heat After pressing, a second layer will be formed during hot pressing, resulting in deterioration of corrosion resistance after painting.

In addition, 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 area where the Fe concentration is 4 mass% or less in the plating is greater than 2.0, the average value of the Si concentration in the plating is low, Therefore, the second phase is not formed. However, the alloy layer peeled off.

100‧‧‧Al-based plated steel plate 101‧‧‧base material 103‧‧‧Al-based plated layer 107‧‧‧surface coating layer 109‧‧‧ZnO particles 111‧‧‧ organic resin

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

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

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

4 is a schematic cross-sectional view of the 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.

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

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

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

100‧‧‧Al series plated steel plate

101‧‧‧ base material

103‧‧‧Al series plating layer

Claims (5)

An Al-based plated steel sheet, characterized in that the average composition of Al contained in the Al-based plated layer is 85% or more by mass%, and Si is 4% or more and 12% or less by mass%, and the plating adheres 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 in mass %, and the Al-based plating layer The ratio of the maximum value of the Si concentration distribution in the 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. The Al-based plated steel sheet according to claim 1, wherein the surface roughness of the Al-based plated layer is an arithmetic average roughness Ra of 0.1 μm or less. The Al-based plated steel sheet according to claim 1 or claim 2, wherein 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 mass% or less is 1.0~1.5. The Al-based plated steel sheet according to claim 1 or claim 2, which has a surface coating layer provided on the Al-based plating layer and containing ZnO particles and an organic resin, and the ZnO particles 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, characterized in that the following steps are performed: In the plating step, the steel sheet is immersed in an Al plating bath containing 6% or more and 15% or less of Si by mass to form a plating Layer; cooling step, cooling the aforementioned steel plate after immersion; etching step, immersing the aforementioned steel plate after cooling in an acidic solution having a pH of 1 or less, etching the surface layer to the following depth: the Si area ratio of the plating surface is 12% or less, When the maximum value of the Si concentration distribution in the thickness direction of the Al-based plating layer is 15% or less in mass %, and the maximum value of the Si concentration distribution and the Fe concentration in the thickness direction of the Al-based plating layer 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.

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