JP2018150593A - FILM COATED HOT-DIP Zn-Al-Mg PLATED STEEL PLATE AND MANUFACTURING METHOD OF THE SAME - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film-coated molten Zn-Al-Mg-based plated steel sheet having a film having excellent slidability, corrosion resistance and appearance, and a method for producing the same. SOLUTION: A molten Zn-Al-Mg-based plated steel sheet having a specific molten Zn-Al-Mg-based plating layer is brought into contact with zinc of 0.01 mol / L or more and less than 10 mol / L for 2 seconds or more and less than 60 seconds. An acid contact step, a drying step of drying the molten Zn-Al-Mg-based plated steel sheet after the acid contact step, and a silane coupling agent (A) on the molten Zn-Al-Mg-based plated steel sheet after the drying step. ), Tetraalkoxysilane (B), zinc compound (C), organic resin (D), wax (E), and a film forming step of applying and drying to form a film. A method for producing a film-coated molten Zn-Al-Mg-based plated steel sheet. [Selection diagram] None

Description

  The present invention relates to a coating-coated hot-dip Zn—Al—Mg-based plated steel sheet excellent in slidability, corrosion resistance and appearance, and a method for producing the same.

  A hot-dip Zn-plated steel sheet (Zn-Al-Mg-based steel sheet) containing Mg and Al has been used for various applications because of its excellent corrosion resistance. In recent years, Zn-Al-Mg-based plated steel sheets with excellent slidability that can withstand more complicated press molding have been desired.

  Patent Document 1 discloses a method of forming Al oxide and Mg oxide having excellent slidability on the surface of a Zn—Al—Mg plated steel sheet.

  However, since the surface of the steel sheet described in Patent Document 1 has only a thin oxide layer and is not covered with a film, there is a problem in corrosion resistance. Further, when the thin oxide layer is repeatedly slid, the oxide layer is peeled off by the first sliding, and the slidability after the second is inferior.

  Patent Document 2 discloses a Zn—Al—Mg plated steel sheet coated with an organic film containing a lubricant.

  Since the steel sheet described in Patent Document 2 has an inorganic film, it exhibits high corrosion resistance, and is excellent in slidability due to the wax contained in the film. However, under severe conditions such as repeated sliding, the soft Zn portion of the Zn—Al—Mg based plating adheres to the mold and the slidability after the second time is lowered.

Japanese Patent No. 5253090 Japanese Patent No. 5901389

  The present invention has been made in view of such circumstances, and an object thereof is to provide a film-coated hot-dip Zn—Al—Mg-based plated steel sheet having a film excellent in slidability, corrosion resistance and appearance, and a method for producing the same. And

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, the above-mentioned problem can be solved by forming a concavo-convex shape on the surface by treating a molten Zn—Al—Mg-based plated steel sheet having a specific plating layer with a specific acid, and further forming a specific film. I found out.

  The present invention has been made based on the above findings, and the gist thereof is as follows.

[1] On at least one surface of the steel sheet, Al: 1.0% by mass or more and less than 5.0% by mass, Mg: 0.2% by mass or more and less than 5.0% by mass, with the balance being Zn and inevitable It has a molten Zn—Al—Mg-based plating layer made of impurities, and the molten Zn—Al—Mg-based plating layer comprises a Zn—Al binary eutectic and an Al—Zn—MgZn ₂ ternary eutectic. An acid contact step in which the molten Zn-Al-Mg-based plated steel sheet is brought into contact with nitric acid of 0.01 mol / L or more and less than 10 mol / L for 2 seconds or more and less than 60 seconds, and molten Zn-Al after the acid contact step -A drying step of drying the Mg-based plated steel plate, and a silane coupling agent (A), a tetraalkoxysilane (B), a zirconium compound (C) on the molten Zn-Al-Mg-based plated steel plate after the drying step, Organic resin (D), wax A method for producing a coating-coated hot-dip Zn—Al—Mg-based plated steel sheet, comprising: applying a coating liquid for forming a coating containing (E) and drying to form a coating.

  [2] The molten Zn—Al—Mg-based plating layer further includes Ni: 0.005 mass% or more and less than 0.1 mass%, and a total of Ce and / or La: 0.005 to 0.05 mass. The method for producing a coating-coated hot-dip Zn—Al—Mg-based plated steel sheet according to [1], wherein at least one of the following is included:

[3] The molten Zn—Al—Mg-based plating layer contains a ternary eutectic of Al—Zn—MgZn _{2 in} a cross section of the plating layer of 10% by area or more and less than 30% by area [1] or [2] The method for producing a coating-coated molten Zn—Al—Mg-based plated steel sheet according to [2].

  [4] The coating-coated hot-dip Zn—Al—Mg-based plated steel sheet according to any one of [1] to [3], wherein an average major axis of the Zn—Al binary eutectic is 10 μm or less. Production method.

[5] On at least one surface of the steel sheet, Al: 1.0% by mass or more and less than 5.0% by mass, Mg: 0.2% by mass or more and less than 5.0% by mass, with the balance being Zn and inevitable A film-coated molten Zn-Al-Mg-based plated steel sheet having a molten Zn-Al-Mg-based plated layer made of impurities and further having a film on the molten Zn-Al-Mg-based plated layer, The Zn—Al—Mg-based plating layer contains a Zn—Al binary eutectic and an Al—Zn—MgZn ₂ ternary eutectic, and the coating comprises a Si compound, a Zr compound, an organic resin, and a wax. wherein, content in terms of SiO ₂ 0.05 g / ^{m 2} or more 3 g / ^m less than ² Si compound, content in terms of ZrO ₂ in 0.05 g / ^{m 2} or more 2 g / ^m less than ² Zr compound, an organic resin 0.05 g / ^{m 2} or more at a content of C in terms Less than 3 g / ^{m 2,} and the thickness of the film is less than 2μm above 0.2 [mu] m, in the cross section of the film-coated hot-dip Zn-Al-Mg plated steel sheet, the maximum Zn-Al-Mg-based plating layer When the thickness is h, the length of the curve formed by the interface between the coating and the molten Zn—Al—Mg-based plating layer in the range of 2 h in the horizontal direction with the steel sheet is L, and of this curve, the coating and the Zn—Al When the sum of the lengths of the curves formed by the interface with which the binary eutectic is in contact is L 1 _Al , the following coating formula (1) and formula (2) are satisfied. Plated steel sheet.
1.5 ≦ L / 2h <5.5 (1)
0.50 ≦ L _Al /L<0.90 (2)
[6] The molten Zn—Al—Mg-based plating layer further includes Ni: 0.005 mass% or more and less than 0.1 mass%, and a total of Ce and / or La: 0.005 to 0.05 mass. %, The film-coated hot-dip Zn-Al-Mg-based plated steel sheet according to [5].

[7] The molten Zn—Al—Mg-based plating layer contains Al—Zn—MgZn ₂ ternary eutectic in a cross section of the plating layer of 10% by area or more and less than 30% by area [5] or The film-coated hot-dip Zn—Al—Mg-based plated steel sheet according to [6].

  [8] The coating-coated molten Zn—Al—Mg-based plated steel sheet according to any one of [5] to [7], wherein an average major axis of the Zn—Al binary eutectic is 10 μm or less.

  According to the present invention, a coating-coated hot-dip Zn—Al—Mg-based plated steel sheet having excellent slidability, corrosion resistance, and appearance can be obtained.

FIG. 1 shows the maximum thickness h of a molten Zn—Al—Mg based plating layer and the interface between the coating and the molten Zn—Al—Mg based plating layer in the cross section of the coated coating hot-dip Zn—Al—Mg based plated steel sheet. It is a schematic diagram illustrating the length L of the curve and the sum L _Al of the lengths of the curves formed by the interface where the coating and the Zn—Al binary eutectic contact each other. FIG. 2 is a schematic front view showing the friction coefficient measuring apparatus. FIG. 3 is a schematic perspective view showing the bead shape and dimensions in FIG.

  Hereinafter, the present invention will be specifically described. In addition, this invention is not limited to the following embodiment.

  The method for producing a coating-coated hot-dip Zn—Al—Mg-based plated steel sheet of the present invention is obtained by applying a specific hot-dip Zn—Al—Mg-based steel sheet to nitric acid of 0.01 mol / L or more and less than 10 mol / L for 2 to 60 seconds. An acid contact step for contacting less than, a drying step for drying the plated steel plate, and a coating forming step for coating the plated steel plate with a coating solution after the drying step and drying to form a coating.

The above-mentioned “specific hot-dip Zn—Al—Mg-based plated steel sheet” means that at least one surface of the steel sheet has Al: 1.0 mass% or more and less than 5.0 mass%, Mg: 0.2 mass% or more. It has a molten Zn-Al-Mg-based plating layer containing less than 0% by mass, the balance being Zn and inevitable impurities, and the molten Zn-Al-Mg-based plating layer is a Zn-Al binary eutectic And a molten Zn—Al—Mg-based plated steel sheet containing a ternary eutectic of Al—Zn—MgZn ₂ .

  In the molten Zn-Al-Mg-based plated steel sheet, Zn-Al binary eutectic fine grains are dispersed in the primary crystal Zn, but the primary Zn is dissolved by bringing it into contact with nitric acid. In addition, the concavo-convex shape is obtained by leaving the Zn—Al binary eutectic. Further, by forming a film on the manufacturing conditions described later, a hot-sliding Zn-Al-Mg-based plated steel sheet can be obtained. The reason why the slidability is improved is not clear, but when sliding using the lubricating oil, the concave and convex portions become oil pockets to hold the lubricating oil and improve the slidability. In addition, since the protrusions are preferentially slid, the contact area between the mold and the steel sheet is reduced, and the sliding resistance is reduced. Furthermore, since the Zn—Al binary eutectic remaining on the surface is harder than Zn, it hardly adheres to the mold, and the increase in sliding resistance is suppressed even when subjected to repeated sliding. Due to these combined effects, the film-coated hot-dip Zn—Al—Mg-based plated steel sheet of the present invention is excellent in slidability even when repeatedly slid.

  First, each structure of the hot-dip Zn—Al—Mg-based plated steel sheet of the present invention will be described.

<Fused Zn-Al-Mg-based plated steel sheet>
The hot-dip Zn—Al—Mg-based plated steel sheet that is the base of the film-coated hot-dip Zn—Al—Mg-based plated steel sheet produced in the present invention will be described. The purpose of adding Mg to the molten Zn-Al-Mg-based plated layer of this molten Zn-Al-Mg-based plated steel sheet is mainly to refine the Zn-Al binary eutectic in the plated layer, An object is to form fine Zn-Al binary eutectic irregularities on the surface by nitric acid dissolution treatment.

  The reason for limiting the component composition of the molten Zn—Al—Mg-based plating layer (hereinafter simply referred to as “plating layer”) will be described.

Al: 1.0% by mass or more and less than 5.0% by mass When the Al content in the plating layer is less than 1.0% by mass, a thick Fe—Zn alloy layer is formed at the plating layer-substrate (steel plate) interface. , Workability decreases. On the other hand, when the Al content is 5.0% by mass or more, a eutectic structure of Zn and Al cannot be obtained, and the Al-rich layer is increased and the sacrificial anticorrosive action is lowered. Moreover, when it is going to obtain the plating layer whose Al content is 5.0 mass% or more, the top dross mainly consisting of Al will generate | occur | produce easily in a plating bath, and the problem that a plating external appearance is impaired also arises. For the above reasons, the Al content in the plating layer is 1.0 mass% or more and less than 5.0 mass%, preferably 2.0 mass% or more and less than 4.0 mass%.

Mg: 0.2 mass% or more and less than 5.0 mass% In the present invention, one of the aims of including Mg in the plating composition is to obtain a fine-grain Zn—Al binary eutectic. The reason why the Zn-Al binary eutectic is refined by the addition of Mg is not clear, but is considered as follows.

The plating layer of a general hot-dip Zn-Al-based plated steel sheet (Al: 4.3 mass%, balance Zn) is composed of a binary eutectic of primary Zn and Zn-Al, and this binary eutectic is the surface of the plating layer. And continuously present in the vicinity of the plating layer-substrate interface. On the other hand, in the plating layer having the composition of the present invention, the ternary eutectic of Al—Zn—MgZn ₂ spreads in the form of a network between primary crystals Zn, and Al is mainly contained in the network. The Zn—Al binary eutectic is scattered finely.

Therefore, in the plated steel sheet of the present invention, it is considered that the ternary eutectic of Al—Zn—MgZn ₂ forms a network during solidification, and the Zn—Al binary eutectic is divided to be finely divided. In addition, the above-mentioned shape is obtained by elemental analysis by SEM-EDX, and the primary crystal Zn portion in which only Zn is detected, the Zn-Al binary eutectic portion in which Zn and Al are detected, and Zn, Al, and Mg The detected ternary eutectic portions of Al—Zn—MgZn ₂ can be confirmed.

When Mg in the plating layer is less than 0.2% by mass, the Zn-Al binary eutectic is not sufficiently refined, the unevenness after the nitric acid treatment is reduced, and sufficient slidability is obtained. Absent. On the other hand, when Mg in the plating layer is 5.0% by mass or more, the Zn—Al binary eutectic becomes fine, but the plating layer hardness increases due to the increase in Al—Zn—MgZn ₂ ternary eutectic. In addition, large cracks are likely to occur during bending, and workability is reduced. Dross adhesion also increases. Therefore, Mg content in a plating layer shall be 0.2 mass% or more and less than 5.0 mass%.

The eutectic ratio of Al—Zn—MgZn ₂ ternary eutectic (the area ratio of the ternary eutectic in the cross section of the plating layer; the same shall apply hereinafter) is preferably 10 area% or more and less than 30 area%. When the eutectic ratio of the ternary eutectic is less than 10% by area, the Zn-Al binary eutectic is not sufficiently refined, the unevenness after nitric acid treatment becomes small, and sufficient slidability cannot be obtained. There is. Further, when the eutectic rate is 30 area% or more, the workability is lowered.

  The average major axis of the binary eutectic of Zn—Al is preferably 10 μm or less. If the average major axis of the Zn—Al binary eutectic is 10 μm or less, sufficient irregularities can be formed after the nitric acid treatment, and sufficient slidability can be obtained by forming a film.

Here, the eutectic ratio of Al—Zn—MgZn ₂ ternary eutectic and the particle size (average major axis) of Zn—Al binary eutectic are measured as follows. In the steel sheet thickness direction cross section SEM, the plating layer excluding the outermost plating layer (region from the surface to 10 μm in the plate thickness direction) in the field of view: vertical: plating layer thickness, horizontal: twice the plating layer thickness Find the internal area. Next, the area of the ternary eutectic of Al—Zn—MgZn ₂ is obtained, and the area ratio of the plating layer is calculated. The average value of 8 fields of view is defined as the eutectic rate. Moreover, about the same cross section SEM, the maximum length of each binary eutectic of Zn-Al is measured as a major axis, and let the average value be an average major axis. These measurements may be made after acid treatment.

  In the plated steel sheet of the present invention, Ni can be contained in the plating layer. By containing Ni, an effect of blackening resistance can be obtained. The Ni content is preferably 0.005% by mass or more and less than 0.1% by mass. When Ni is less than 0.005% by mass, the effect of improving blackening resistance cannot be obtained, and when it is 0.1% by mass or more, Al—Mg-based dross containing Ni is generated in the plating bath, and the plating appearance due to dross adhesion is impaired. Therefore, it is not preferable.

  In the plated steel sheet of the present invention, a misch metal containing Ce and / or La can be contained in the plating layer. The misch metal containing Ce and / or La has an effect of increasing the fluidity of the plating bath, preventing the occurrence of fine non-plated pinholes, and uniforming the plating unevenness.

  When the misch metal content is less than 0.005 mass% in terms of the total amount of Ce and La, the effect of suppressing pinholes cannot be sufficiently obtained, and the effect of uniforming the plating unevenness is lost. On the other hand, if the total amount of Ce and La exceeds 0.05% by mass, it will be present as an undissolved suspended matter in the plating bath, which will adhere to the plated surface and impair the plating appearance. That is, if the content of misch metal is 0.005% by mass or more in terms of the total amount of Ce and La, a pinhole suppressing effect can be sufficiently obtained, and the surface smoothing is effective, while Ce and If the total amount of La is 0.05% by mass or less, they will not be present as undissolved suspended matter in the plating bath, and undissolved suspended matter will not adhere to the plating surface and impair the plating appearance. . For this reason, the misch metal containing Ce and / or La is preferably 0.005 to 0.05% by mass, more preferably 0.007 to 0.02% by mass in terms of the total amount of Ce and La. .

  Note that the plating layer contains Al and Mg as described above, Ni is contained if necessary, and further, misch metal containing Ce and / or La is contained if necessary, and the balance is Zn and inevitable. It is an impurity.

  As described above, a plating composition in which fine eutectic Zn-Al binary eutectic is dispersed in the primary Zn phase by adding an appropriate amount of Mg to the plating layer of the molten Zn-Al-Mg based steel sheet. Have. Moreover, the hot-dip Zn-Al-Mg type plated steel plate without unplating, such as a micro pinhole, can be obtained by containing a proper amount of misch metal containing Ce and / or La as required.

  The above-described molten Zn—Al—Mg-based plated steel sheet and film-coated molten Zn—Al—Mg-based plated steel sheet can be obtained, for example, under the following production conditions.

  The steel plate used as the base steel plate may be appropriately selected from known steel plates depending on the application, and is not particularly limited. For example, it is preferable to use a low carbon aluminum killed steel plate or an ultra low carbon steel plate from the viewpoint of plating work. This steel plate (underlying steel plate) is immersed in a hot-dip Zn-Al plating bath and subjected to hot-dip (hot) plating, and then cooled by pulling up from the plating bath, and a hot-dip Zn-Al alloy plating layer is formed on the steel plate surface. Form. This plating layer contains Al: 1.0% by mass or more and less than 5.0% by mass, Mg: 0.2% by mass or more and less than 5.0% by mass, and further contains Ce and / or La as necessary. The misch metal is 0.005 to 0.05% by mass in terms of the total amount of Ce and La, and the balance is made of Zn and inevitable impurities. Therefore, it is preferable to adjust the bath composition of the molten Zn—Al plating bath so as to be substantially the same as the average composition of the plating layer.

  The cooling rate of the plated steel sheet pulled up from the molten Zn—Al-based plating bath is not particularly limited, but the cooling rate up to 250 ° C. is preferably 1 to 15 ° C./second, and preferably 2 to 10 ° C./second. If the cooling rate of the plated steel sheet pulled up from the plating bath to 250 ° C. is less than 1 ° C./second, a Zn—Al binary eutectic may not be generated. On the other hand, when the cooling rate exceeds 15 ° C./second, Zn—Al binary eutectic grains tend to be large.

  The plating bath temperature is preferably in the range of 390 to 500 ° C. When the plating bath temperature is less than 390 ° C., the viscosity of the plating bath increases and the plating surface tends to become uneven. On the other hand, when the plating bath temperature exceeds 500 ° C., dross in the plating bath tends to increase. That is, if the plating bath temperature is 390 ° C. or higher, the viscosity of the plating bath is properly maintained, so that the plating surface is less likely to be uneven, while if it is 500 ° C. or lower, dross in the plating bath increases. Hateful.

Acid contact step The acid contact step is a step in which a molten Zn-Al-Mg based plated steel sheet is brought into contact with nitric acid of 0.01 mol / L or more and less than 10 mol / L for 2 seconds or more and less than 60 seconds.

By bringing the plating layer of the above-mentioned molten Zn-Al-Mg-based steel sheet into contact with nitric acid, the primary Zn in the plating surface layer (area from the surface of the plating layer up to 10 μm in the plate thickness direction) is dissolved and refined. The Zn—Al binary eutectic thus formed remains on the surface, and fine irregularities are formed. Since the Zn—Al binary eutectic remaining on the surface is harder than Zn and has excellent corrosion resistance, the resulting surface is also excellent in slidability and corrosion resistance. In addition, since the ternary eutectic of network Al—Zn—MgZn ₂ is not dissolved in nitric acid, the fine particles of Zn—Al binary eutectic are formed as ternary eutectic of network Al—Zn—MgZn _2. The concavo-convex shape can maintain sufficient strength.

  Hereinafter, the reason for limitation of the nitric acid treatment method will be described.

  If the nitric acid concentration is less than 0.01 mol / L, the effect of dissolution is small, and an uneven shape cannot be obtained. Preferably it is 0.1 mol / L or more. On the other hand, in the case of 10 mol / L or more, the dissolution rate is fast, the uneven shape becomes too large and the appearance becomes uneven, so the concentration of nitric acid is less than 10 mol / L. Preferably it is 1 mol / L or less.

  The contact time with nitric acid is 2 seconds or more and less than 60 seconds. If it is less than 2 seconds, the treatment time is short, and an uneven shape cannot be obtained. On the other hand, if it is 60 seconds or longer, the processing time is long, the productivity is lowered, and the uneven shape becomes too large, leading to a deterioration of the appearance.

  The temperature of the acid is not particularly specified, and may be 5 ° C. or higher and lower than 70 ° C. as a general range. Although the acid can be used by heating, the effect of promoting dissolution by heating is small.

  There is no restriction | limiting in particular about the method of making a steel plate contact with nitric acid. A roll coating method, a bar coating method, a dipping method, a spray coating method, or the like can be used. After contacting the steel sheet with the acid, the acid is washed away with water within the range of the contact time and dried. This corresponds to the drying step in the present invention.

Film Forming Process The film forming process is a process in which a film forming treatment liquid is applied to the molten Zn—Al—Mg-based plated steel sheet after the drying process and dried to form a film.

  The film forming treatment liquid contains a silane coupling agent (A), a tetraalkoxysilane (B), a zirconium compound (C), an organic resin (D), and a wax (E).

  Examples of the silane coupling agent (A) include vinylmethoxysilane, vinylethoxysilane, vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, β- (3,4 epoxycyclohexyl) ethyltrimethoxysilane, γ- Glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane, N-β (aminoethyl) γ-aminopropylmethyldimethoxysilane, N-β (aminoethyl) ) -Γ-aminopropylmethyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropylmethyltrimethoxysilane, γ- Tacryloxypropylmethyldiethoxysilane, γ-methacryloxypropylmethyltriethoxysilane, γ-mercaptopropylmethyldimethoxysilane, γ-mercaptopropylmethyltrimethoxysilane, p-styryltrimethoxysilane, γ-acryloxypropyltrimethoxysilane N-phenyl-γ-aminopropyltrimethoxysilane, γ-ureidopropyltriethoxysilane, γ-chloropropyltrimethoxysilane, bis (triethoxysilylpropyl) tetrasulfide, γ-isocyanatopropyltriethoxysilane, γ-tri Ethoxysisilyl-N- (1,3-dimethyl-butylidene) propylamine, N- (vinylbenzylamine) -β-aminoethyl-γ-aminopropyltrimethoxysilane and the like, It can be used one or more these. In particular, a silane coupling agent having an amino group or an epoxy group is preferable.

  The silane coupling agent (A) can be crosslinked with a tetraalkoxysilane (B) described later to obtain a very dense and excellent surface-treated film that can withstand repeated sliding. The silane coupling agent (A) is preferably 8% or more and less than 50% of the total solid content in the treatment liquid.

  The tetraalkoxysilane (B) is not particularly limited as long as it contains four lower alkoxyl groups (for example, methoxy group, ethoxy group, propoxy group) as hydrolyzable groups in one molecule. The four lower alkoxyl groups may be all or partly the same or all different. Examples thereof include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and the like, and one or more of these can be used. Of these, the use of tetraethoxysilane and / or tetramethoxysilane is preferred.

  Tetraalkoxysilane (B) is an extremely dense Si compound, which is hydrolyzed when dissolved in water to produce a silanol group. This silanol group crosslinks with the silane coupling agent (A), so that a very dense surface-treated film excellent in adhesiveness that can withstand repeated sliding is obtained. The tetraalkoxysilane (B) is preferably 2% or more and less than 30% of the total solid content in the treatment liquid.

  The zirconium compound (C) is not particularly limited. For example, zirconium acetate, zirconium propionate, zirconium oxychloride, zirconium nitrate, zirconium carbonate ammonium, zirconium carbonate potassium, zirconium zirconium chloride, zirconium sulfate, zirconium phosphate, sodium zirconium phosphate , Potassium hexafluorozirconium, tetranormal propoxyzirconium, tetranormalbutoxyzirconium, zirconium tetraacetylacetonate, zirconium tributoxyacetylacetonate, zirconium tributoxy systemate, and the like can be used alone. Or two or more of them may be used in combination. Of these, ammonium zirconium carbonate and potassium zirconium carbonate are preferred from the viewpoint of stability in an aqueous solvent.

  Such a zirconium compound (C) has a strong binding force with oxygen and can be strongly bonded to an oxide or hydroxide on the surface of the molten Zn—Al—Mg-based steel sheet. Further, since such a zirconium compound (C) has 4 or more, generally 6 to 8 bonds, it forms a dense and repetitive slide by forming a network with Zr compounds and other inorganic compounds. A film that can withstand movement can be formed. The zirconium compound (C) is preferably 8% or more and less than 50% of the total solid content in the treatment liquid.

  The organic resin (D) is not particularly limited, and examples thereof include aqueous resins (emulsions) such as acrylic resins, alkyd resins, polyolefin resins, styrene resins, vinyl acetate resins, epoxy resins, phenol resins, polyester resins, urethane resins, and melamine resins. And dispersion may be used, and these may be used alone or in combination of two or more. Among these, a polyester resin, an acrylic resin, an epoxy resin, and a urethane resin are preferable because the corrosion resistance becomes better.

  The organic resin (D) is essential from the viewpoint of imparting flexibility to the film and improving the throwing power to the unevenness of the plating, and is preferably 10% or more and less than 75% of the total solid content in the treatment liquid. .

  The wax (E) is not particularly limited as long as it is compatible with the liquid. For example, polyolefin wax such as polyethylene, montan wax, paraffin wax, microcrystalline wax, carnauba wax, lanolin wax, silicon wax, A fluorine-type wax etc. are mentioned, These 1 or more types can be used. Examples of the polyolefin wax include polyethylene wax, polyethylene oxide wax, and polypropylene wax, and one or more of these can be used. Of these, polyethylene wax is preferred because it concentrates on the outermost surface of the film and exhibits high slidability.

  The wax (E) is essential from the viewpoint of imparting slidability to the film, and is preferably 0.1% or more and less than 5% of the total solid content in the treatment liquid.

  The method of forming the film is not particularly limited, and examples thereof include a method of immersing the zinc-based plated steel sheet in a treatment liquid capable of forming a film, and a method of applying the treatment liquid to the zinc-based plated steel sheet. . The treatment liquid coating method may be appropriately selected depending on the shape of the zinc-plated steel sheet to be treated, and the water- and oil-repellent treatment liquid may be selected by roll coating, bar coating, dipping, spray coating, or the like. It is possible to apply. Furthermore, it is possible to adjust the coating amount, uniform appearance, and uniform film thickness by air knife method or roll drawing method after coating. In addition, what is necessary is just to prepare a process liquid by a conventionally well-known method.

  In addition, the drying method after processing with the process liquid which can form the said film | membrane is not specifically limited, Room temperature drying or heat drying may be sufficient. As a means for performing heat drying, a dryer, a hot air furnace, a high frequency induction heating furnace, an infrared furnace, or the like can be used. Although it does not specifically limit about temperature, It is preferable that it is about room temperature-about 200 degreeC in the highest plate | board temperature (Peak Metal Temperature: PMT).

The film-coated hot-dip Zn-Al-Mg-plated steel sheet formed in this way has a film and molten Zn content in the range of 2 h in the steel sheet width direction when the maximum thickness of the hot-dip Zn-Al-Mg-based plating layer is h. -The length of the curve formed by the interface with which the interface of the Al-Mg plating layer is in contact is L, and among these curves, the binary eutectic of the film and Zn-Al (that is, the molten Zn-Al-Mg plating layer When the sum of the lengths of the curves formed by the interface with which the projections are in contact is L _Al , the following expressions (1) and (2) are satisfied.
1.5 ≦ L / 2h <5.5 (1)
0.50 ≦ L _Al /L<0.90 (2)
L / 2h is an index of surface unevenness, and the film-coated hot-dip Zn—Al—Mg-based plated steel sheet exhibits high slidability within the range of the formula (1). If L / 2h is less than 1.5, the unevenness effect is small, and the slidability decreases. On the other hand, when L / 2h is 5.5 or more, the unevenness is too large, so that the surface pressure is partially increased and the slidability due to repeated sliding is lowered, and the appearance is deteriorated due to light absorption by the unevenness. Preferably, it is 1.7 or more and less than 3.0. L _Al / L is an index of the amount of Al on the surface of the plating layer, and within the range of the formula (2), the film-coated hot-dip Zn—Al—Mg based steel sheet exhibits high slidability and good appearance. When L _Al / L is less than 0.50, a lot of soft Zn is present on the surface, so that the slidability when repeatedly sliding becomes insufficient. When L _Al / L is 0.90 or more, the surface is melted and the unevenness is too large, so that the appearance deteriorates. Preferably, it is 0.6 or more and less than 0.8.

In addition, about h, L, and L _Al as shown in FIG. 1, length: a cross section in the thickness direction of the steel sheet in any five fields of view: plating layer thickness, width: twice the plating layer thickness in the width direction of the steel sheet SEM is observed, the average value of the five visual fields of the maximum thickness of the plating layer is set as h, and the average value of the five visual fields of the length of the curve formed by the interface between the coating and the molten Zn-Al-Mg plating layer is set as L. The average value of the five fields of view of the sum of the lengths of the curves formed by the interface where the coating and the Zn—Al binary eutectic are in contact can be calculated as L _Al .

Furthermore, the film of the coating-coated hot-dip Zn—Al—Mg plated steel sheet formed in this way contains a Si compound, a Zr compound, an organic resin, and a wax, and the content of the Si compound is 0.05 g / in terms of SiO _2. m ² or more 3 g / ^m less than ^2, the content is 0.05 g / ^{m 2} or more 2 g / ^m less than ² in terms of ZrO ₂ of Zr compound, the content of the organic resin is 0.05 g / ^{m 2} or more calculated as C 3 g / The film thickness is less than m ² and the film thickness is 0.2 μm or more and less than 2 μm.

When the content is less than 0.05 g / ^{m 2} or more 3 g / ^{m 2} in terms of SiO ₂ of the Si compound, Zr compound, by using a composite with an organic resin, a good dense film having adhesion to the plating layer And has excellent slidability. The content of the Si compound is insufficient in adhesion of the coating and the plating layer is less than 0.05 g / ^{m 2} in terms of SiO _2, inferior in sliding resistance when subjected to repeated sliding, coating in a 3 g / ^{m 2} or more In addition, the Zr compound, the organic resin and the unreacted Si compound remain, resulting in poor corrosion resistance. Preferably, SiO ₂ converted at 0.1 g / ^{m 2} to less than 1 g / ^{m 2.}

When the content of Zr compound is a 2 g / ^m less than ² 0.05 g / ^{m 2} or more in terms of ZrO _2, Si compounds, by using a composite with an organic resin, a good dense film having adhesion to the plating layer And has excellent slidability. The content of Zr compound is insufficient in adhesion of the coating and the plating layer is less than 0.05 g / ^{m 2} in terms of ZrO _2, inferior in sliding resistance when subjected to repeated sliding, coating in a 2 g / ^{m 2} or more Si compound, organic resin and unreacted Zr compound remain, resulting in poor slidability and corrosion resistance. Preferably, ZrO ₂ converted at 0.1 g / ^{m 2} to less than 1 g / ^{m 2.}

If the content of the organic resin is 0.05 g / m ² or more and less than 3 g / m ^{2 in} terms of C, a dense film with good adhesion to the plating layer can be obtained by using it in combination with the Si compound and Zr compound. It can be formed and has excellent slidability. In addition, the inclusion of an organic resin imparts flexibility to the coating, and the throwing power to the unevenness of plating is improved, resulting in excellent slidability and corrosion resistance. If the content of the organic resin is less than 0.05 g / m ^{2 in} terms of C, the film is inferior in flexibility and the film cannot follow the unevenness, so that it is inferior in slidability and corrosion resistance, and if it is 3 g / m ² or more, The film is soft and cannot withstand repeated sliding. Preferably, C converted at 0.1 g / ^{m 2} to less than 1 g / ^{m 2.}

  The content of such Si compound, Zr compound, and organic resin is determined by analyzing the film using fluorescent X-rays, measuring the strength of each element, and using a calibration curve prepared using steel plates with known contents. It can be calculated from the intensity.

  Moreover, if the film thickness is 0.2 μm or more and less than 2 μm, a film excellent in slidability and corrosion resistance can be obtained. If the thickness is less than 0.2 μm, the coating is partially insufficiently covered and the sliding property and corrosion resistance are poor. If it is 2 μm or more, the film thickness unevenness of the film is noticeable and the appearance is poor. Preferably, the film thickness is 0.4 μm or more and less than 1 μm. In addition, a film thickness can be calculated | required from the SEM observation of the cross section of a coating-coating molten Zn-Al-Mg type plated steel plate.

  Next, the present invention will be specifically described based on examples. However, the present invention is merely an example for explaining the present invention, and the present invention is not limited thereto.

  Each plated steel sheet used as a base steel sheet for a surface-treated plated steel sheet (corresponding to a coating-coated hot-dip Zn-Al-Mg based steel sheet) It is shown in Table 1 together with the subsequent cooling rate to 250 ° C.

Here, the eutectic ratio of Al—Zn—MgZn ₂ ternary eutectic (area ratio of the ternary eutectic in the cross section of the plating layer (X% in Table 1)) and Zn—Al binary eutectic The particle size (average major axis (Y μm in Table 1)) was measured by the method described above.

Nitric acid is sprayed on the plated steel sheet for a predetermined time, then water is sprayed and washed with water, and then dried with a blower. And dried so that the maximum temperature reached 80 ° C. in 5 to 20 seconds to obtain a test material. L / 2h and L _Al / L were measured by the method described above. These specimens were evaluated for slidability, corrosion resistance, and appearance by the following test methods. The results are shown in Table 3 together with the nitric acid concentration applied to each test material, the composition of the surface treatment composition and the coating conditions.

(1) Sliding property In order to evaluate press formability, the friction coefficient of each test material was measured as follows. FIG. 2 is a schematic front view showing the friction coefficient measuring apparatus. As shown in the figure, a friction coefficient measurement sample 1 collected from a test material is fixed to a sample table 2, and the sample table 2 is fixed to the upper surface of a slide table 3 that can move horizontally. A slide table support 5 having a roller 4 in contact with the slide table 3 is provided on the lower surface of the slide table 3, and the pressing load N applied to the friction coefficient measurement sample 1 by the bead 6 is measured by pushing it up. A first load cell 7 is attached to the slide table support 5. A second load cell 8 is attached to one end of the slide table 3 in order to measure the sliding resistance force F when the slide table 3 is moved in the horizontal direction with the pressing force applied. . In addition, the cleaning oil Preton R352L for press made by Sugimura Chemical Co., Ltd. as a lubricating oil was applied to the surface of the friction coefficient measurement sample 1 and tested.
FIG. 3 is a schematic perspective view showing the shape and dimensions of the beads used. The bead 6 slides with its lower surface pressed against the surface of the sample 1. The bead 6 shown in FIG. 3 has a width of 10 mm, a length of 59 mm in the sliding direction of the sample, and a lower portion at both ends in the sliding direction is formed by a curved surface having a curvature of 4.5 mmR. It has a plane with a direction length of 50 mm.
The friction coefficient measurement test was performed under the following conditions.
Using the bead shown in FIG. 3, the pressing load N was set to 400 kgf, the sample drawing speed (horizontal moving speed of the slide table 3): 20 cm / min, and the same sample was slid continuously five times. During the sliding, the bead was not wiped off.
The coefficient of friction μ between the test material and the bead was calculated by the formula: μ = F / N, and an average value of five times of sliding was used. The evaluation criteria are as follows.
◎ Friction coefficient is less than 0.10 ○ Friction coefficient is 0.10 or more and less than 0.13 △ Friction coefficient is 0.13 or more (2) Corrosion resistance and appearance JIS- A salt spray test of Z-2371-2000 was performed, and the test time at which the white rust generation area ratio was 5% was measured. The evaluation criteria are as follows.

：: 240 hours or more ○: 192 hours or more, less than 240 hours ○-: 120 hours or more, less than 192 hours Δ: less than 120 hours In addition, the appearance was visually observed and evaluated after the salt spray test. The evaluation criteria are as follows.
◎: White taste, no unevenness ○: Gray taste, no unevenness ○-: Gray taste, unevenness △: Grayish black taste

  From the results in Table 3, it was found that all the samples of the present invention were excellent in slidability, corrosion resistance and appearance. On the other hand, it was found that the sample of the comparative example lacking any of the requirements could not obtain a satisfactory result for any of the performances.

  According to the present invention, it is possible to obtain a coating-coated hot-dip Zn—Al—Mg-based plated steel sheet having excellent slidability, corrosion resistance, and appearance.

DESCRIPTION OF SYMBOLS 1 Friction coefficient measurement sample 2 Sample stand 3 Slide table 4 Roller 5 Slide table support stand 6 Bead 7 1st load cell 8 2nd load cell 9 Rail N Pushing load F Sliding resistance force

Claims (8)

At least one surface of the steel sheet contains Al: 1.0% by mass or more and less than 5.0% by mass, Mg: 0.2% by mass or more and less than 5.0% by mass, with the balance being Zn and inevitable impurities. A molten Zn-Al-Mg-based plating layer, the molten Zn-Al-Mg-based plating layer containing a Zn-Al binary eutectic and an Al-Zn-MgZn ₂ ternary eutectic An acid contact step of contacting a Zn-Al-Mg based steel sheet with nitric acid of 0.01 mol / L or more and less than 10 mol / L for 2 seconds or more and less than 60 seconds;
A drying step of drying the molten Zn-Al-Mg based steel sheet after the acid contact step;
A silane coupling agent (A), a tetraalkoxysilane (B), a zirconium compound (C), an organic resin (D), and a wax (E) are contained on the molten Zn—Al—Mg plated steel sheet after the drying step. A method for producing a coating-coated molten Zn-Al-Mg-based plated steel sheet, comprising: a coating forming step of applying a coating liquid for forming a coating and drying to form a coating.   The molten Zn—Al—Mg-based plating layer further includes Ni: 0.005% by mass or more and less than 0.1% by mass, and a total of Ce and / or La: 0.005 to 0.05% by mass. The method for producing a coating-coated hot-dip Zn—Al—Mg-based plated steel sheet according to claim 1, comprising at least one. The molten Zn—Al—Mg-based plating layer contains a ternary eutectic of Al—Zn—MgZn _{2 in} an area of 10% to less than 30% by area of the plating layer. The manufacturing method of the coating-coating hot-dip Zn-Al-Mg type plated steel plate.   The average major axis of the Zn-Al binary eutectic is 10 µm or less, The method for producing a coating-coated hot-dip Zn-Al-Mg-based plated steel sheet according to any one of claims 1 to 3. At least one surface of the steel sheet contains Al: 1.0% by mass or more and less than 5.0% by mass, Mg: 0.2% by mass or more and less than 5.0% by mass, with the balance being Zn and inevitable impurities. A coating-coated molten Zn-Al-Mg-based plated steel sheet having a molten Zn-Al-Mg-based plating layer and further having a film on the molten Zn-Al-Mg-based plating layer,
The molten Zn—Al—Mg-based plating layer contains a Zn—Al binary eutectic and an Al—Zn—MgZn ₂ ternary eutectic,
The coating, Si compounds, Zr compounds and organic resin comprises a wax, the content of Si compound 0.05 g / ^{m 2} or more 3 g / ^m less than ² in terms of SiO _2, the content of Zr compound in terms of ZrO ₂ 0.05 g / ^{m 2} or more 2 g / ^m than ^2, the content of the organic resin is 0.05 g / ^{m 2} or more 3 g / ^m below ² C terms and thickness of the film is less than 2μm above 0.2μm Yes,
When the maximum thickness of the molten Zn-Al-Mg-based plating layer is h in the cross section of the coating-coated molten Zn-Al-Mg-based plated steel sheet, the film and the molten Zn-Al- When the length of the curve formed by the interface of the Mg-based plating layer is L, and the sum of the lengths of the curves formed by the interface between the coating and the Zn—Al binary eutectic is L _Al A film-coated hot-dip Zn—Al—Mg-based plated steel sheet characterized by satisfying the following formulas (1) and (2):
1.5 ≦ L / 2h <5.5 (1)
0.50 ≦ L _Al /L<0.90 (2)   The molten Zn—Al—Mg-based plating layer further includes Ni: 0.005% by mass or more and less than 0.1% by mass, and a total of Ce and / or La: 0.005 to 0.05% by mass. The coating-coated hot-dip Zn—Al—Mg-based plated steel sheet according to claim 5, comprising at least one. The molten Zn—Al—Mg-based plating layer contains a ternary eutectic of Al—Zn—MgZn _{2 in} an area of 10% by area or more and less than 30% by area in the plating layer cross section. Coating-coated hot-dip Zn-Al-Mg-based plated steel sheet.   The average long diameter of the Zn-Al binary eutectic is 10 µm or less, and the film-coated hot-dip Zn-Al-Mg-based plated steel sheet according to any one of claims 5 to 7.

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