JP6939825B2 - Al-based galvanized steel sheet and its manufacturing method - Google Patents

Description

The present invention relates to an Al-based plated steel sheet and a method for producing the same.

Traditionally, Zn-based plated steel sheets in which the surface of steel materials are plated with Zn or Zn-based alloys have been used in a wide range of fields such as automobiles, home appliances, and building materials. Due to problems such as resource depletion, a metal for rust-preventive plating that replaces Zn is required.

Al has abundant reserves, and Al-plated steel sheets plated with Al have excellent corrosion resistance without painting, and are therefore widely used as structural materials for home appliances and buildings. Like the Al-plated steel sheet, the Al-Zn alloy-plated steel sheet has excellent corrosion resistance and is widely used as a structural material for home appliances and buildings. For example, Patent Document 1 states that "Si: 3 to 13% by mass, Ni: 0.03% by mass or less, Cu: 0.05% by mass or less, the balance is composed of Al and unavoidable impurities, and Ni. An aluminum-plated steel sheet having excellent corrosion resistance, characterized in that a molten aluminum-plated layer having a total amount of Cu and a total amount of 0.07% by mass or less is formed on the surface of the steel sheet, is described.

However, when Al-plated steel sheets and Al-Zn alloy-plated steel sheets are coated and used, coating film swelling occurs starting from coating scratches due to chipping or the like, or shear ends with poor coating turnability, resulting in Zn. It has a problem that it is inferior in corrosion resistance after painting to a galvanized steel sheet. This is because in Al-plated steel sheets and Al-Zn alloy-plated steel sheets, the single-phase Al (α-Al) present in the plating layer is inferior to Zn in alkali resistance, and alkalization has progressed due to the corrosion reaction under the coating film. This is because the single-phase Al is actively dissolved in. Therefore, it is difficult to replace zinc-based plating having excellent post-painting corrosion resistance with conventional Al-plated steel sheets and Al—Zn alloy-plated steel sheets.

Further, in the resistance spot welding used for assembling the vehicle body, the Al-plated steel sheet and the Al—Zn alloy-plated steel sheet are extremely inferior to the Zn-based plated steel sheet. This is because the electrical resistance of Al is small and a large current is required for heat generation for welding, and the reaction between the molten single-phase Al and the electrode metal is remarkable, so it is necessary to increase the frequency of electrode maintenance. This is because it is inferior in sex.

In recent years, Al-based plated steel sheets having improved corrosion resistance or resistance spot weldability after painting have been proposed. Patent Document 2 states that "in mass%, one or two of Fe: 1 to 75%, Mg: 0.02 to 50% and Ca: 0.02 to 1%, and the balance: Al and unavoidable. "Aluminum-based alloy-plated steel material having excellent corrosion resistance at the cut end face and corrosion resistance at the processed portion, which is characterized by having a plating film composed of target impurities" is described.

Patent Document 3 states that "in mass%, one or two of Fe: 1 to 75%, Cr: 0.02 to 10% and Ni: 0.02 to 10%, and the balance: Al and unavoidable. "Aluminum-based alloy-plated steel material having excellent oxidation resistance and spot weldability, which is characterized by having a plating film composed of target impurities" is described.

Japanese Unexamined Patent Publication No. 2001-214249 Japanese Unexamined Patent Publication No. 2009-120942 Japanese Unexamined Patent Publication No. 2009-120943

However, the technique described in Patent Document 1 has the following problems. Patent Document 1 aims to suppress the formation of the Fe—Al—Si alloy layer by adding Si to the plating bath. On the alloy layer, a thick plating layer mainly composed of metal Al which is not alloyed with Fe is formed. Al, which is not alloyed with Fe, is very excellent in corrosion resistance of the unpainted flat plate portion. Therefore, for example, in applications such as building materials, suppressing the formation of an alloy layer can be said to be an effective means for improving corrosion resistance. However, assuming an automobile body, firstly, Al not alloyed with Fe has a low melting point, and for example, it melts during resistance spot welding and adheres to the electrode metal, resulting in a significant deterioration in electrode life. In addition, as a result of examining the corrosion behavior according to the actual appearance corrosion environment of the automobile, it was found that the base steel plate and the base steel plate form a galvanic pair in the corroded state under the coating film, and the environment is alkalized. A plated steel sheet having Al that is not alloyed with Fe on the surface layer is inferior in corrosion resistance in an alkaline environment to a Zn-based plated steel sheet that is generally used as a rust-preventive steel sheet for automobiles. Will also be inferior. Therefore, the Al-based plated steel sheet in which Si is added to the plating bath to suppress the formation of the Fe—Al—Si alloy layer has problems in resistance spot weldability and post-painting corrosion resistance.

In the technique described in Patent Document 2, Mg and / or Ca are added in order to enhance the corrosion resistance of the cut end face and the corrosion resistance of the processed portion. However, the corrosion resistance of the cut end face and the corrosion resistance of the processed part are evaluated by the salt spray test (SST), which is a constant wetting process, and the composite cycle corrosion test (CCT), in which the ratio of the wetting process is significantly larger than the actual corrosion environment of the automobile outer panel. Has been done. In the evaluation by the present inventors based on the corrosion test method based on the corrosive environment of the automobile outer panel, which has a long drying process, the effect of adding Mg and / or Ca was not observed, and sufficient post-painting corrosion resistance was obtained. In some cases, it was found that there is room for improvement in post-painting corrosion resistance in an environment that conforms to the corrosive environment of automobile outer panels. Further, in the technique described in Patent Document 3, Cr and / or Ni are added in order to enhance the oxidation resistance of the plating film. However, since both Cr and Ni are environmentally hazardous substances, alternative technologies are desired in consideration of their versatility as structural materials for automobiles. Further, as in Patent Document 2, in the evaluation based on the corrosion test method in accordance with the corrosion environment of the automobile outer panel, which has a long drying process, sufficient corrosion resistance after painting may not be obtained, and the automobile outer panel is corroded. It was found that there is room for improvement in the corrosion resistance after painting in an environment that is in line with the environment.

Therefore, in view of the above problems, it is an object of the present invention to provide an Al-based plated steel sheet having excellent post-painting corrosion resistance and resistance spot weldability in an environment suitable for the corrosive environment of an automobile outer plate, and a method for producing the same.

As a result of diligent studies by the present inventors in order to solve the above problems, the following findings were obtained. That is, (i) an Al—Fe alloy plating layer having a predetermined thickness is formed on the surface of the base steel plate, and a predetermined amount of Ca is contained in the Al—Fe alloy plating layer, and (ii) the Al—Fe alloy. By limiting the amount of Al adhering to the surface of the plating layer, which does not form an intermetallic compound with Fe, to ^{the range of 1000 mg / m 2} or less, after painting in an environment that conforms to the corrosive environment of the automobile outer panel. It was found that both corrosion resistance and resistance spot weldability can be achieved.

The abstract structure of the present invention completed based on the above findings is as follows.
(1) Base steel plate and
At least one side of the base steel sheet contains, in mass%, Fe: 40 to 70%, Ca: 1.5 to 10%, and has a component composition in which the balance is Al and unavoidable impurities, and has a thickness of 7 to 30 μm. Al-Fe-Ca alloy plating layer and
Al adhering to the surface of the Al—Fe—Ca alloy plating layer, having an adhering amount of 0 to 1000 mg / m ² , and not forming an intermetallic compound with Fe,
An Al-based plated steel sheet characterized by having.

(2) The component composition of the Al—Fe—Ca alloy plating layer further contains, in mass%, at least one selected from Mg, Zn, Sn, Mn, and Cr in a total of 10% or less (1). ). Al-plated steel sheet.

(3) The base steel sheet is immersed in a hot-dip galvanized bath having a component composition of Fe: 5% or less, Ca: 3.0 to 20%, and the balance of Al and unavoidable impurities in mass%, and then gas. A method for producing an Al-based plated steel sheet, which comprises producing the Al-based plated steel sheet according to (1) above by performing wiping.

(4) The method for producing an Al-based plated steel sheet according to (3) above, wherein after the gas wiping, an alloying treatment of Al by heating is performed.

(5) The component composition of the hot-dip plating bath further contains at least 20% or less in total of at least one selected from Mg, Zn, Sn, Mn, and Cr in mass%, as described in (2) above. The method for producing an Al-based plated steel sheet according to (3) or (4) above, which manufactures the Al-based plated steel sheet according to the above.

The Al-plated steel sheet of the present invention is excellent in both post-painting corrosion resistance and resistance spot weldability in an environment suitable for the corrosive environment of automobile outer panels. Further, according to the method for producing an Al-based plated steel sheet of the present invention, it is possible to produce an Al-based plated steel sheet having excellent post-painting corrosion resistance and resistance spot weldability in an environment suitable for the corrosive environment of an automobile outer plate.

In the present specification, "%" representing the content of the component composition means "mass%" unless otherwise specified.

(Al-plated steel sheet)
The Al-based plated steel sheet according to the embodiment of the present invention includes a base steel sheet, an Al—Fe—Ca alloy plating layer having a predetermined component composition and a thickness of 7 to 30 μm on at least one surface of the base steel sheet, and the Al— It is characterized by having Al adhering to the surface of the Fe—Ca alloy plating layer, having an adhering amount of 0 to 1000 mg / m ² , and not forming an intermetallic compound with Fe.

[Al-Fe-Ca alloy plating layer]
In the present embodiment, the Al—Fe—Ca alloy plating layer has a component composition containing Fe: 40 to 70% and Ca: 1.0 to 10%, the balance being Al and unavoidable impurities, and per side. The thickness of is 7 to 30 μm.

Fe: 40-70%
When the Fe content in the Al-Fe-Ca alloy plating layer is less than 40%, an Al-Fe alloy phase mainly composed of Al ₄ Fe _{13 having a relatively low melting point is formed, which melts during resistance spot welding.} It adheres to the electrode, the life of the electrode is extremely shortened, and the resistance spot weldability is reduced. On the other hand, when the Fe content in the Al—Fe—Ca alloy plating layer exceeds 70%, the anticorrosion effect of the base iron by Al cannot be sufficiently obtained, and the corrosion resistance after coating and the corrosion resistance of the mating portion are lowered. Therefore, the Fe content in the Al—Fe—Ca alloy plating layer is set to 40% or more and 70% or less.

Ca: 1.5-10%
When the Ca content in the Al—Fe—Ca alloy plating layer is less than 1.5%, the natural potential of the plating layer in salt water has almost no potential difference from the underlying steel sheet, or becomes a more noble potential. In this case, the anticorrosive effect due to the excellent barrier property is expected, but if the plating is missing due to processing or chipping, the underlying steel sheet is corroded starting from the missing part, and the sacrificial anticorrosive effect of the plating layer can be sufficiently obtained. However, the corrosion resistance after painting and the corrosion resistance of the mating part are reduced. Therefore, the Ca content is 1.5% or more, preferably 2.5% or more, and more preferably 3.5% or more. Further, when the Ca content in the Al—Fe—Ca alloy plating layer exceeds 10%, the Al—Fe alloy phase becomes extremely brittle, and the resistance spot weldability and the corrosion resistance after coating deteriorate. Therefore, the Ca content is 10% or less, preferably 8% or less, and more preferably 5% or less.

The rest other than Fe and Ca are Al and unavoidable impurities. However, it is preferable that the component composition of the Al—Fe—Ca alloy plating layer further contains at least one selected from Mg, Zn, Sn, Mn, and Cr in a total of 10% or less. By containing these elements together with Ca, the growth promoting effect of the Al—Fe alloy phase by Ca in the molten metal is synergistically enhanced, and excellent corrosion resistance at the mating portion can be obtained.

Thickness 7 to 30 μm (per side)
When the thickness of the Al-Fe-Ca alloy plating layer is less than 7 μm, the corrosion rate when forming a galvanic pair with the base steel plate becomes significantly high in the places where the plating is defective, such as the end face, the flawed part, and the chipping part. Corrosion resistance and mating part corrosion resistance deteriorate after painting. Further, when the thickness of the Al—Fe—Ca alloy plating layer exceeds 30 μm, a high current is required to melt the plating layer during resistance spot welding, so that the resistance spot weldability deteriorates. Therefore, the thickness of the Al—Fe—Ca alloy plating layer is set to 7 μm or more and 30 μm or less.

In the present invention, the "thickness of the Al-Fe-Ca alloy plating layer" is determined by using an optical microscope, an electron probe microanalyzer (EPMA), a scanning electron microscope-energy dispersive X-ray analyzer (SEM-EDS), or the like. Can be measured. Considering the variation in the plating thickness in the sample, the sample is taken from any 3 or more points in the same plane, and the average plating thickness in the sample is obtained by observing and averaging 3 or more visual fields in each. do. In order to easily know the thickness of the plating layer, a glow discharge emission analyzer (GDS) or an electromagnetic induction type or magnetic type film thickness meter may be used.

[Al that does not form an intermetallic compound with Fe]
The Al that does not form an intermetallic compound with Fe is mainly a metal Al that is not alloyed with Fe, and also contains Al that exists as an Al—Ca alloy.

Adhesion amount per side: 0 to 1000 mg / m ²
When the amount of Al adhering to one side, which does not form an intermetallic compound with Fe ^{, exceeds 1000 mg / m 2} , preferential corrosion occurs in a corrosive environment under the coating film, and the corrosion resistance after coating deteriorates. Further, by melting during resistance spot welding, the electrode adheres to the electrode, the life of the electrode is extremely shortened, and the resistance spot weldability is lowered. Therefore, in the present embodiment, it is important that the amount of adhesion of Al, which does not form an intermetallic compound with Fe, per one side is 1000 mg / m ^{2 or less.} When the adhesion amount is 1000 mg / m ² or less, Al which does not form an intermetallic compound with Fe is scattered on the surface of the Al—Fe—Ca alloy plating layer in a granular or island shape. .. It is preferably 200 mg / m ² or less, and more preferably 100 mg / m ² or less. The lower limit of the adhered amount is not particularly limited, and the adhered amount may be 0 mg / m ² or more.

In the present invention, the "adhesion amount of Al that does not form an intermetallic compound with Fe per one side" is determined by the following method. That is, one side of the Al-based galvanized steel sheet is subjected to constant current electrolysis at a current density of ^{4 mA / cm 2 in a 0.01 M NaOH aqueous solution.} At that time, the amount of electricity in the time region showing the potential in the range of −0.9 V or less with respect to the Ag—AgCl electrode was converted into the amount of Al, and the obtained amount of Al was used to “form an intermetal compound with Fe. The amount of adhesion of Al per one side was not set. _{That is, the amount of Al} (g / m ² ) that does not form an intermetallic compound with Fe is _{w Al} = Q × M, where Q (C) is the amount of electricity in the range of −0.9 V or less. _{It is calculated by Al} / (3 × F × S). Here, M _Al is the molar mass of Al (g / mol), F is the Faraday constant (C / mol), and S is the test piece area (m ² ). When the amount of adhesion is different on the front and back surfaces, it is possible to measure the amount of adhesion on each surface by performing constant current electrolysis on each surface.

[Base steel plate]
The type of base steel sheet used in the present invention is not particularly limited. For example, a hot-rolled steel sheet or steel strip obtained by pickling and descaling, or a cold-rolled steel plate or steel strip obtained by cold-rolling them can be used. The hot rolling step may be carried out by a usual method of winding through slab heating, rough rolling, and finish rolling. Further, the heating temperature, the finish rolling temperature, and the like are not particularly specified, and can be carried out at a normal temperature. The pickling step performed after hot rolling may also be performed by a commonly used method, and examples thereof include washing with hydrochloric acid, sulfuric acid, or the like. The cold rolling step performed after pickling is also not particularly limited, but can be performed at a rolling reduction rate of, for example, 30 to 90%. If the rolling reduction is 30% or more, the mechanical properties do not deteriorate, while if it is 90% or less, the rolling cost does not increase.

(Manufacturing method of Al-based plated steel sheet)
The method for producing an Al-plated steel sheet according to an embodiment of the present invention has a component composition in which the base steel sheet contains Fe: 5% or less and Ca: 3.0 to 20%, and the balance is Al and unavoidable impurities. It can be produced by immersing it in a hot-dip plating bath, then performing gas wiping, preferably after gas wiping, and then performing an alloying treatment of Al by heating.

According to this method, an Al—Fe—Ca alloy plating layer is formed on the surface of the steel sheet while the base steel sheet is immersed in the molten Al-based plating bath. Immediately after the base steel sheet is pulled out of the plating bath and before gas wiping, the Al—Fe—Ca alloy plating layer and the molten Al—Ca are present in the upper layer thereof. The molten Al—Ca present on this surface is gas-wiped to adjust the amount of Al adhering to Fe, which does not form an intermetallic compound, to 0 to 1000 mg / m ² . After that, if Al—Ca is alloyed by heating, the amount of Al adhering to Fe, which does not form an intermetallic compound, can be more easily set to 0 to 1000 mg / m ² .

The component composition of the plating bath needs to contain Fe: 5% or less, Ca: 3.0 to 20%, and the balance is Al and unavoidable impurities. This provides a 7-30 μm thick Al—Fe—Ca alloy plating layer containing Fe: 40-70%, Ca: 1.5-10%, and a component composition with the balance being Al and unavoidable impurities. This is to form. In particular, Si suppresses the alloying reaction between Al in the plating bath and Fe in the base steel sheet, and therefore, in order to form an Al—Fe—Ca alloy plating layer having a thickness of 7 to 30 μm, it is intentional in the plating bath. It is necessary not to contain it in. In addition, this plating bath may inevitably contain 5% or less of Fe eluted from the base steel sheet, but this is allowed in the present invention.

Further, the component composition of the plating bath preferably contains at least one selected from Mg, Zn, Sn, Mn, and Cr in a total of 20% or less. As a result, an Al—Fe—Ca alloy plating layer containing at least 10% or less of at least one selected from the above-mentioned Mg, Zn, Sn, Mn, and Cr can be formed.

In order to make the Fe content of the Al-Fe-Ca alloy plating layer 40 to 70% and the thickness 7 to 30 μm, the temperature of the Al-Ca plating bath and the temperature of the base steel plate to the Al-Ca plating bath It is preferable to appropriately control the immersion time. The higher the bath temperature, the higher the rate of the Al—Fe—Ca alloying reaction on the surface of the base steel sheet, so that the productivity in the case of thickening is improved. On the other hand, if the bath temperature is too high, the plating bath surface will be heavily oxidized. In view of the above, the temperature of the Al—Ca plating bath is preferably 680 ° C. or higher and 720 ° C. or lower. It is more preferably 690 ° C. or higher and 715 ° C. or lower, and further preferably 700 ° C. or higher and 710 ° C. or lower. Further, the longer the immersion time, the more the Al—Fe—Ca alloying progresses on the surface of the base steel sheet, and the Fe content of the Al—Fe—Ca alloy plating layer increases. In order to control the Fe content to 40 to 70% and the thickness to 7 to 30 μm, the immersion time of the base steel sheet in the Al—Ca plating bath is preferably 0.5 seconds or more and 30 seconds or less. It is more preferably 1 second or more and 20 seconds or less, and further preferably 2 seconds or more and 10 seconds or less. Examples of the intermetallic compound constituting the Al—Fe—Ca alloy plating layer include Fe ₄ Al ₁₃ , Fe ₂ Al ₅ , _{Fe Al 2} , Fe Al, and Fe _{3 Al.} The existence form of Ca is not clear, but it is presumed that it is solid-solved by substituting the Fe or Al sites of the intermetallic compound.

The amount of adhesion of Al that does not form an intermetallic compound with Fe per side is the flow rate of wiping gas, line speed, gas pressure of gas wiping, nozzle shape, distance between nozzle and steel plate, plating bath surface and wiping device. It can be adjusted according to the distance to and the like, and it is preferable to appropriately determine the conditions so that the target adhesion amount is 0 to 1000 mg / m ^2. For example, by increasing the flow rate of the wiping gas, it is possible to reduce the amount of Al adhering to Fe, which does not form an intermetallic compound. The flow rate of the wiping gas is preferably 300 L / min or more, more preferably 500 L / min or more, still more preferably 1000 L / min or more, and most preferably 2000 L / min or more. The wiping gas is preferably an inert gas such as _{N 2 gas.} Further, by lowering the line speed, it is possible to reduce the amount of Al that does not form an intermetallic compound with Fe. The line speed is preferably 200 m / min or less, more preferably 120 m / min or less, still more preferably 60 m / min or less.

Alloying treatment When Al that does not form an intermetallic compound with Fe remains on the surface layer, one side of Al that does not form an intermetallic compound with Fe is performed by performing a heat treatment to alloy the Al. The amount of adhesion per hit can be more easily set to 1000 mg / m ² or less. The method of alloying treatment is not particularly limited, but for example, it can be carried out by box annealing (BAF annealing), or can be carried out continuously by induction heating or the like after Al plating in a continuous hot-dip plating facility. Al can be incorporated into the Al—Fe—Sn alloy plating layer by raising the temperature of the Al-based plated steel sheet to 450 to 950 ° C. at a heating rate of 50 ° C./h to 50 ° C./s. In heating in a continuous hot-dip plating facility, the ultimate plate temperature is preferably 750 ° C. or higher. In the case of box annealing, it is preferable that the plate temperature is 450 to 600 ° C. and the retention time in the temperature range is 1 to 50 hours in an atmosphere containing oxygen: 3% by volume or more.

According to the method for producing an Al-plated steel sheet of the present embodiment described above, Fe: 40 to 70% and Ca: 1.5 to 10% in mass% on the base steel sheet and at least one surface of the base steel sheet. Amount of adhesion to the surface of the Al-Fe-Ca alloy plating layer having a thickness of 7 to 30 μm and the Al-Fe-Ca alloy plating layer having a component composition in which the balance is Al and unavoidable impurities. To produce an Al-based plated steel sheet having excellent post-coating corrosion resistance and resistance spot weldability, which comprises 0 to 1000 mg / m ^{2 of Al which does not form an intermetallic compound with Fe.} Can be done.

The Al-based plated steel sheet of the present embodiment and the Al-based plated steel sheet produced by the manufacturing method of the present embodiment can also be suitably used as a hot-pressed steel sheet. Generally, in order to produce a hot-pressed member having a beautiful appearance and excellent corrosion resistance using an Al-based plated steel sheet, the plated steel sheet is heated before the hot-pressing to bring the plated layer to its surface with Al having a high melting point. It is effective to use a −Fe alloy. The Al-based plated steel sheet of the present embodiment and the Al-based plated steel sheet manufactured by the manufacturing method of the present embodiment are sufficiently provided with an Al—Fe alloyed plating layer in advance before heating before hot pressing. It is formed. Therefore, even when the temperature rise rate is increased or the holding time is shortened during heating before hot pressing to improve productivity, heat having excellent coating adhesion and post-coating corrosion resistance is obtained. The inter-press member can be stably manufactured.

A cold-rolled steel sheet having a thickness of 0.8 mm manufactured by a conventional method was used as a base steel sheet. This cold-rolled steel sheet was annealed for 30 seconds in a nitrogen atmosphere containing 5% by volume of hydrogen at 800 ° C. and a dew point of −30 ° C., and cooled with nitrogen gas until the plate temperature reached 700 ° C. Then, the cold-rolled steel sheet was immersed in a molten Al-based plating bath having the component composition shown in Table 1, and then N ₂ gas wiping was performed to obtain a level No. Al-plated steel sheets 1 to 56 were produced. The "Fe content" and "thickness" of the Al—Fe—Ca alloy plating layer were controlled by appropriately adjusting the bath temperature and the immersion time. Further, the amount of adhesion of Al, which does not form an intermetallic compound with Fe, per one side was controlled by adjusting the flow rate of the wiping gas and the line speed. At some levels shown in Table 1, the sample after plating was alloyed by heating it in a muffle furnace at an atmospheric temperature of 500 ° C. for 60 minutes.

The composition of the components of the plating bath was confirmed by collecting about 2 g from the plating bath and conducting a chemical analysis. The composition of each level of plating bath is shown in Table 1. Regarding the composition of the plating layer, any three cross sections were cut out from the Al-based plated steel sheet of each level by shearing, embedded in carbon resin, and then SEM observed, and measured by EDX at any five points of the plating layer. The average value of the semi-quantitative analysis values was used. Table 1 shows the composition of the plating layer at each level (the rest is Al and unavoidable impurities).

Further, the thickness of the Al—Fe—Ca alloy plating layer per one side and the amount of adhesion of Al not forming an intermetallic compound with Fe per one side were measured by the method described above. The results are shown in Table 1.

(Evaluation of resistance spot weldability)
At each level, the continuous dot weldability in the overlay welding of two plated steel sheets having a plate thickness of 0.8 mm was evaluated. Welding power supply: single-phase AC, electrode material: Cu-Cr alloy, electrode shape: dome shape, electrode tip diameter: 6 mm, pressing force: 2400 N, welding time: 10 cycles (frequency: 50 Hz), welding angle Not provided. First, resistance welding was performed by changing the welding current, and the current at which the formed welding nugget diameter was 4√t (t: thickness of the plated steel sheet), that is, 3.6 mm was defined as I ₀ . 1.4 times the current I ₀ as I _a, to perform continuous welding tests in current I _a, weld nugget diameter was determined number of consecutive RBI to less than 4√T. The evaluation was carried out by setting the following four-stage evaluation criteria, and ○ or higher was regarded as acceptable. The results are also shown in Table 1.
⊚: Over 2500 ○: 1000-2500
Δ: 500 to 1000
×: Less than 500

(Evaluation of corrosion resistance after painting)
A sample obtained by cutting a plated steel sheet of each level into a size of 70 mm × 80 mm was subjected to zinc phosphate treatment as a chemical conversion treatment and then electrodeposition coating in the same manner as the coating treatment for automobile outer panels. Here, the zinc phosphate treatment and electrodeposition coating were performed under the following conditions.
[Zinc phosphate treatment]
A steel sheet was subjected to chemical conversion treatment using a commercially available chemical conversion treatment agent (Palbond SX-35 manufactured by Nihon Parkerizing Co., Ltd.) under the conditions of a bath temperature of 35 ° C., a free fluorine concentration of 200 mass ppm, and a treatment time of 120 seconds.
[Electrodeposition coating]
Electrodeposition coating manufactured by Kansai Paint Co., Ltd .: Using GT-100, the voltage was adjusted so that the film thickness was 15 μm, and electrodeposition coating was applied.

After chemical conversion treatment and electrodeposition coating, the edge of the evaluation surface (one side) is 7.5 mm and the non-evaluation surface (other surface) is sealed with tape, and then the base of the plated steel sheet is placed in the center of the evaluation surface with a cutter knife. A cross-cut scratch with a length of 60 mm and a central angle of 60 ° was added to a depth reaching the steel plate to prepare a sample for evaluation. Using the above evaluation sample, a corrosion acceleration test was carried out in the cycle specified in SAE J2334. After starting the corrosion acceleration test from wetting and performing it after 60 cycles, the coating film swelling width of the part where the coating film swelling from the scratched part is the maximum (maximum coating film swelling width: maximum on one side with the scratched part in the center) The coating film swelling width) was measured, and the corrosion resistance after coating was evaluated according to the following criteria. The evaluation was carried out by setting the following four-stage evaluation criteria, and ○ or higher was regarded as acceptable. The results are shown in Table 1.
⊚: Maximum coating film swelling width ≤ 2.0 mm
◯: 2.0 mm <maximum coating film swelling width ≤ 3.0 mm
Δ: 3.0 mm <maximum coating film swelling width ≤ 4.0 mm
X: 4.0 mm <maximum coating film swelling width

(Evaluation of corrosion resistance at the mating part)
A large plate of 70 mm x 80 mm and a small plate of 40 mm x 60 mm are cut out from the plated steel plate with a plate thickness of 0.8 mm produced at each level, and the small plates are overlapped with the central part of the large plate and subjected to resistance spot welding. Samples were prepared by joining at the points. The sample was subjected to zinc phosphate treatment as a chemical conversion treatment and then electrodeposition coating in the same manner as the coating treatment for automobile outer panels. Here, the zinc phosphate treatment and electrodeposition coating were performed under the following conditions.
[Zinc phosphate treatment]
A steel sheet was subjected to chemical conversion treatment using a commercially available chemical conversion treatment agent (Palbond SX-35 manufactured by Nihon Parkerizing Co., Ltd.) under the conditions of a bath temperature of 35 ° C., a free fluorine concentration of 200 mass ppm, and a treatment time of 120 seconds.
[Electrodeposition coating]
Electrodeposition coating manufactured by Kansai Paint Co., Ltd .: Using GT-100, the voltage was adjusted so that the film thickness was 15 μm, and electrodeposition coating was applied.

It was confirmed that there was no chemical conversion treatment or electrodeposition coating inside the steel sheet mating. An evaluation sample was prepared by sealing the end 5 mm of the evaluation surface (one side) and the non-evaluation surface (other surface) with tape. Using the above evaluation sample, a corrosion acceleration test was carried out in the cycle specified in SAE J2334. After starting the corrosion acceleration test from wetting and performing it after 150 cycles, the spot welds are disassembled, the electrodeposition coating on the large plate is peeled off using a coating film remover, and then the large plate is added to hydrochloric acid to which an inhibitor is added. By immersing the plate, corrosion products mainly composed of iron were removed. After that, the corrosion depth was measured using a point micrometer, and the corrosion resistance of the mating part was evaluated according to the following criteria. The evaluation was carried out by setting the following four-stage evaluation criteria, and ○ or higher was regarded as acceptable. The results are shown in Table 1.
⊚: Maximum corrosion depth <0.2 mm
◯: 0.2 mm ≤ maximum corrosion depth <0.4 mm
Δ: 0.4 mm ≤ maximum corrosion depth <0.8 mm
×: Maximum corrosion depth = 0.8 mm (perforated)

In the example of the present invention, both corrosion resistance after painting and resistance spot weldability were excellent. On the other hand, in the comparative example, at least one of the corrosion resistance after painting and the resistance spot weldability was inferior.

The Al-plated steel sheet of the present invention is excellent in both post-painting corrosion resistance and resistance spot weldability in an environment suitable for the corrosive environment of automobile outer panels. Further, according to the method for producing an Al-based plated steel sheet of the present invention, it is possible to produce an Al-based plated steel sheet having excellent post-painting corrosion resistance and resistance spot weldability in an environment suitable for the corrosive environment of an automobile outer plate.

Claims (5)

Base steel plate and
At least one side of the base steel sheet contains, in mass%, Fe: 40 to 70%, Ca: 1.5 to 10%, and has a component composition in which the balance is Al and unavoidable impurities, and has a thickness of 7 to 30 μm. Al-Fe-Ca alloy plating layer and
Al adhering to the surface of the Al—Fe—Ca alloy plating layer, having an adhering amount of 0 to 1000 mg / m ² , and not forming an intermetallic compound with Fe,
An Al-based plated steel sheet characterized by having. Claim 1 that the component composition of the Al—Fe—Ca alloy plating layer further contains at least one selected from Mg, Zn, Sn, Mn, and Cr in a mass% of more than 0% and 10% or less in total. The Al-based plated steel sheet described in 1. The base steel sheet is immersed in a hot-dip galvanized bath containing Fe: 5% or less and Ca: 3.0 to 20% in mass%, and the balance is Al and an unavoidable impurity component composition, and then gas wiping is performed. A method for producing an Al-based plated steel sheet, which comprises producing the Al-based plated steel sheet according to claim 1. The base steel sheet contains Fe: 5% or less, Ca: 3.0 to 20% in mass%, and at least one selected from Mg, Zn, Sn, Mn, and Cr in mass% in total. 0% greater than or less seen containing 20%, the balance being immersed in a molten plating bath having a chemical composition of Al and unavoidable impurities, followed by performing gas wiping, producing an Al-based plated steel sheet according to claim 2 A method for manufacturing an Al-based plated steel sheet. The method for producing an Al-based plated steel sheet according to claim 3 or 4 , wherein the Al alloying treatment is performed by heating after the gas wiping.