KR20170120165A - Zn-Mg alloy coated steel sheet - Google Patents

Abstract

The Zn-Mg alloy-plated steel sheet comprises a steel sheet, a Zn-Mg alloy plating layer formed on the surface of the steel sheet and containing 10 to 70 mass% of Mg and the balance of Zn and impurities, A corrosion product layer formed on the surface of the alloy plating layer and containing either a Mg salt of a carboxylic acid having 4 to 20 carbon atoms and an Mg salt of an alkanesulfonic acid having 4 to 20 carbon atoms; Wherein the corrosion product layer contains an alkali metal salt of the carboxylic acid when the corrosion product layer contains the magnesium salt of the carboxylic acid and the corrosion product layer contains the magnesium salt of the alkanesulfonic acid, Wherein the alkali metal salt of the carboxylic acid or the alkali metal salt of the alkali metal salt of the alkanesulfonic acid contained in the chemical conversion treatment layer is at least one selected from the group consisting of Li, Na, K, Rb Is at least one member selected from the group consisting of Cs.

Description

Zn-Mg alloy coated steel sheet

The present invention relates to a Zn-Mg alloy plated steel sheet.

The present application claims priority based on Japanese Patent Application No. 2015-78585 filed on April 7, 2015, the contents of which are incorporated herein by reference.

Plating may be applied to the steel used for automobiles, home appliances, building materials, etc. to improve corrosion resistance. The plating layer formed on the surface of the steel material by plating is roughly classified into two types: a barrier-type plating layer type that shields the steel material from the external environment and a sacrificial-type plating layer type that forms the steel material by corrosion prior to the substrate. Zn is conventionally used for plating steel, but the plating layer formed by Zn plating is classified as a sacrificial plating layer type.

When a steel sheet having a plated layer formed on its surface (hereinafter referred to as a plated steel sheet) is used for a long period of time, surface treatment such as painting treatment, chemical treatment, or lamination is performed on the surface of the plated steel sheet . The chemical treatment mainly aims to improve the primary rustproofing property of the surface of the coated steel sheet during the process until the coated steel sheet is processed and assembled and becomes the final product. In the chemical conversion treatment, a layer having a suitable adhesion with the surface of the plating layer (hereinafter referred to as a chemical conversion treatment layer) is formed on the surface of the plating layer.

Recently, as disclosed in Patent Documents 1 to 4, there has been proposed a Zn-Mg alloy-plated steel sheet in which a plating layer containing a Zn-Mg alloy is formed on the surface of a steel sheet instead of a Zn-coated steel sheet in order to improve corrosion resistance . The Zn-Mg alloy coated steel sheet has better corrosion resistance than the Zn-coated steel sheet by stabilizing the corrosion products generated under the corrosive environment by Mg.

Japanese Patent Application Laid-Open No. 2005-146340 Japanese Patent Application Laid-Open No. 2007-23309 Japanese Patent Application Laid-Open No. 2010-248541 Japanese Patent Application Laid-Open No. 2011-219823

As described above, the Zn-Mg alloy plated steel sheet has excellent corrosion resistance as compared with the Zn-plated steel sheet. However, when the Zn-Mg alloy-plated steel sheet is subjected to the conversion treatment used for the Zn-plated steel sheet, when the Zn-Mg alloy-plated steel sheet is discolored to black (hereinafter referred to as blackening phenomenon) (Hereinafter referred to as " expansion forming phenomenon "), there is a case that proper primary rustproofing property can not be obtained.

It is also believed that the blackening phenomenon is attributable to the fact that the Mg ions eluted from the plated layer form an auxiliary ratio oxide and the expansion formation phenomenon is caused by the Mg ions eluted from the plating layer continuously forming an unstable corrosion product.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a Zn-Mg alloy plated steel sheet having a chemically treated layer having excellent primary rustproofing property.

The present inventors have studied a method of improving the primary rustproofing property by forming a stable corrosion product by Mg ions eluted from a Zn-Mg alloy. As a result, the inventors of the present invention found that the Mg dissolved from the plating layer under the corrosive environment and the material eluted from the chemical conversion treatment layer are combined with each other by incorporating a substance having a small solubility of the Mg salt and high solubility of the alkali metal salt in the chemical conversion treatment layer, It has been found that the corrosion part of the plating layer is covered by the corrosion product, so that the phenomenon of blackening or expansion can be suppressed.

Further, the inventors of the present invention have conducted further studies to find that the alkali metal salt of a carboxylic acid having 4 to 20 carbon atoms or the alkaline metal salt of an alkane sulfonic acid having 4 to 20 carbon atoms is contained in the converted layer of the Zn- And the primary rustproofing property is remarkably improved. Thus, the present invention has been accomplished.

The present invention solves the above problems and adopts the following means in order to achieve this object.

(1) A Zn-Mg alloy-plated steel sheet according to one aspect of the present invention is a Zn-Mg alloy-plated steel sheet comprising a steel sheet, a Zn-Mg alloy coating layer formed on the surface of the steel sheet and containing 1.0 to 70.0 mass% of Mg and the balance of Zn and impurities. Mg alloy plating layer and a corrosion product layer formed on the surface of the Zn-Mg alloy plating layer and containing either a Mg salt of a carboxylic acid having 4 to 20 carbon atoms and an Mg salt of an alkanesulfonic acid having 4 to 20 carbon atoms And a corrosion product layer formed on the surface of the corrosion product layer, wherein the corrosion product layer contains an alkali metal salt of the carboxylic acid when the corrosion product layer contains the Mg salt of the carboxylic acid, And a chemical conversion layer containing an alkaline metal salt of an alkane sulfonic acid when the salt contains a salt, wherein the alkali metal salt of the carboxylic acid or the alkali metal salt of the alkane sulfonic acid The alkali metal is at least one selected from the group consisting of Li, Na, K, Rb and Cs.

(2) In the Zn-Mg alloy-plated steel sheet according to (1), the Zn-Mg alloy plating layer may contain Mg in an amount of 5.0 to 70.0 mass%.

(3) In the Zn-Mg alloy-plated steel sheet according to (2), the Zn-Mg alloy plating layer may contain Mg in an amount of 10.0 to 70.0 mass%.

(4) In the Zn-Mg alloy-plated steel sheet according to (3), the Zn-Mg alloy plating layer may contain Mg in an amount of 15.0 to 70.0 mass%.

(5) The Zn-Mg alloy plated steel sheet according to any one of the above-mentioned (1) to (4), wherein the Zn-Mg alloy plating layer contains 0.3 to 25.0% by mass of Al, 0.01 to 5.00% , 1.0 to 5.0 mass% of Ca, and 0.1 to 1.5 mass% or less of Ni.

(6) In the Zn-Mg alloy-plated steel sheet according to any one of the above-mentioned (1) to (5), the alkali metal may be Na.

(7) The Zn-Mg alloy-plated steel sheet according to (6), wherein the content of the alkali metal salt of the carboxylic acid or the alkali metal salt of the alkane sulfonic acid contained in the converted layer is 10 to 1500 Mg / m < 2 > may be employed.

(8) In the Zn-Mg alloy-plated steel sheet according to any one of the above-mentioned (1) to (7), the carbonic acid or the alkane sulfonic acid may have a carbon number of 5 to 20.

(9) In the Zn-Mg alloy-plated steel sheet according to (8), the carbonic acid or the alkanesulfonic acid may have a carbon number of 8 to 12.

(10) In the Zn-Mg alloy-plated steel sheet according to any one of the above-mentioned (1) to (9), a structure in which the carboxylic acid is a saturated fatty acid may be adopted.

(11) In the Zn-Mg alloy-plated steel sheet according to any one of the above-mentioned (1) to (10), the chemical conversion treatment layer may not contain fluoride, trivalent chromium and vanadium.

According to each of the above-described embodiments, it is possible to provide a Zn-Mg alloy plated steel sheet having a chemically treated layer having excellent primary rustproofing properties.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram showing the layer structure of a Zn-Mg alloy plated steel sheet according to the present embodiment. Fig.

Hereinafter, a Zn-Mg alloy plated steel sheet according to the embodiment and a manufacturing method thereof will be described with reference to the drawings.

[Zn-Mg alloy-plated steel sheet (1)]

Fig. 1 is a schematic view showing the layer structure of a Zn-Mg alloy-plated steel sheet 1. Fig. The Zn-Mg alloy-plated steel sheet 1 comprises a steel sheet 2 and a Zn-Mg alloy alloy layer 10 formed on the surface of the steel sheet 2 and containing 10 to 70 mass% of Mg and the balance of Zn and impurities A plating layer 3 and a Mg salt of a carboxylic acid having 4 to 20 carbon atoms and an Mg salt of an alkanesulfonic acid having 4 to 20 carbon atoms, which are formed on the surface of the Zn-Mg alloy plating layer 3 Wherein the corrosion product layer (4) is formed on the surface of the corrosion product layer (4) and the corrosion product layer (4) contains an alkali metal salt of a carboxylic acid when it contains the Mg salt of a carboxylic acid, When the layer (4) contains an Mg salt of an alkanesulfonic acid, a chemical conversion layer (5) containing an alkaline metal salt of an alkanesulfonic acid is provided.

In the conventional Zn-Mg alloy plated steel sheet 1, when the converted layer 5 was formed on the Zn-Mg alloy plated layer 3, the phenomenon of blackening or expansion was remarkable. However, even when the chemical conversion treatment layer 5 is formed, the Zn-Mg alloy-plated steel sheet 1 according to the present embodiment suppresses the formation of the secondary oxidation oxide of Mg and the formation of unstable corrosion products, Has been improved.

As described later in detail, by containing an alkali metal salt of a carboxylic acid or alkanesulfonic acid having 4 to 20 carbon atoms in the chemical conversion treatment layer 5, the above-mentioned primary rustproofing effect can be improved. Mg ions eluted from the Zn-Mg alloy plating layer 3 under the chemical conversion treatment and the corrosive environment and the carboxylic acid ions or alkanesulfonic acid ions eluted from the chemical conversion treatment layer 5 are bonded to each other to form a stable corrosion product of carboxylic acid Mg salt of alkanesulfonic acid or Mg salt of alkanesulfonic acid is produced. The Mg salt of the resulting carboxylic acid or the Mg salt of the alkanesulfonic acid precipitates in layers on the Zn-Mg alloy plating layer 3 to form a corrosion product layer 4. [ A carboxylic acid or alkanesulfonic acid having 4 to 20 carbon atoms bonds with Mg to form a Mg salt, particularly covering the corrosion part. As a result, elution of Mg ions from the Zn-Mg alloy plating layer 3 is suppressed.

≪ Zn-Mg alloy plating layer (3) >

The Zn-Mg alloy plating layer 3 contains a Zn-Mg alloy, and may contain at least one or more selected from the group consisting of Al, Si, Ca and Ni, if necessary. It may contain about 0 to 5 mass% of elements such as Y, La, Ce, Ti, Cr, Fe, Co, V, Nb, Cu, Sn, Mn, Sr, Sb and Pb.

Hereinafter, the contents of Mg, Al, Si, Ca, and Ni will be described. In addition, the remainder other than these alloying elements include Zn and impurities. Here, the impurity is a component incorporated by various factors of the raw material and the manufacturing process, and is a so-called inevitable impurity. The balance other than the above alloying element is preferably composed of Zn and inevitable impurities.

≪ Mg: 1.0 to 70.0 mass%

Mg (magnesium) is a major element constituting the Zn-Mg alloy plating layer 3 together with Zn. The content of Mg in the Zn-Mg alloy plating layer 3 is set to 1.0 mass% or more in order to improve the sacrificial corrosion resistance. Preferably, the content of Mg is 5% by mass or more, more preferably 10% by mass or more, further preferably 15% by mass or more. On the other hand, if the content of Mg exceeds 70.0 mass%, the Mg phase is crystallized in the Zn-Mg alloy plating layer 3 and the corrosion resistance remarkably decreases, which is not preferable.

As described later, Mg in the Zn-Mg alloy plating layer 3 reacts with the carboxylic acid or alkane sulfonic acid coated on the surface to form Mg salt. This Mg salt has an effect of further improving the corrosion resistance of the Zn-Mg alloy layer 3 as compared with the case where there is no Mg salt. It is for this reason that the above-mentioned preferable Mg concentration further improves the corrosion resistance, and it exerts more effects than the corrosion resistance obtained by simply increasing the Mg concentration (Tanaka).

When the Zn-Mg alloy plating layer 3 does not contain Mg, the Mg salt of the carboxylic acid or alkanesulfonic acid to be described later is not formed, so that the corrosion product layer 4 is not formed. Therefore, it is not preferable because appropriate corrosion resistance can not be obtained.

≪ Al: 0.30 to 25.0 mass%

Al is an element for improving the corrosion resistance of the flat portion of the Zn-Mg alloy plating layer 3. In order to obtain this effect, it is preferable that 0.30 mass% or more of Al is contained in the Zn-Mg alloy plating layer 3. On the other hand, if the content of Al exceeds 25.0 mass%, red rust easily occurs and corrosion resistance may be lowered. Therefore, the upper limit is preferably 25.0 mass% or less. Considering the adhesion of the converted layer 5 to the Zn-Mg alloy plating layer 3, the content of Al is more preferably 20.0 mass% or less.

≪ Si: 0.010 to 5.0 mass%

Si is an element for suppressing the growth of the alloy phase formed at the interface between the steel sheet 2 and the Zn-Mg alloy plating layer 3 and preventing the deterioration of the workability. The Si is added to the Zn-Mg alloy plating layer 3 in an amount of 0.010% Or more. When the Si content exceeds 5.0 mass%, the bottom dross is easily formed in the plating bath and the workability is lowered. Therefore, the Si content is preferably 5.0 mass% or less.

≪ Ca: 1.0 to 5.0 mass%

Ca is added to the Zn-Mg alloy plating layer 3 as needed in order to improve the operability of the hot-dip coating. In producing the Zn-Mg alloy plated steel sheet 1 according to the present embodiment, a Mg-containing alloy is used as a plating bath. In order to form an oxide film suitable for the surface of the Mg-containing alloy in a molten state, it is preferable to add Ca, which is an element effective for preventing Mg oxidation, in an amount of 1.0% by mass or more. Since Ca may deteriorate corrosion resistance when the content of Ca is large, it is preferable to set the upper limit of Ca content in the Zn-Mg alloy plating layer 3 to 5.0 mass%.

≪ Ni: 0.10 to 1.50 mass%

Ni is an element that improves the wettability upon plating. Mg alloy plating layer 3 is formed on the Ni-plated steel sheet 2 in advance, the steel sheet 2 and the Zn-Mg alloy layer 3 are formed more easily than when the Zn-Mg alloy plating layer 3 is formed on the steel sheet 2. [ The formation of the Al-Fe intermetallic compound in the vicinity of the interface of the alloy plating layer 3 is suppressed, and the workability is improved. On the other hand, if the content of Ni is large, the corrosion resistance may deteriorate. Therefore, it is preferable to set the upper limit of the content of Ni in the Zn-Mg alloy plating layer 3 to 1.50%. The content of Ni in the Zn-Mg alloy plating layer 3 is preferably 0.10% by mass or more.

Ni may be included in the plated alloy as the preliminary Ni plating as described above, or may be included as one component in the plating alloy in advance.

The Zn-Mg alloy plating layer 3 may contain elements constituting the steel sheet 2 as a base material. Particularly, when the Zn-Mg alloy plating layer 3 is formed by the hot dip coating method or when the heat treatment is performed after the Zn-Mg alloy plating layer 3 is formed, the interface between the steel sheet 2 and the Zn-Mg alloy plating layer 3 The elements are mutually diffused. In such a case, the adhesion between the steel sheet 2 and the Zn-Mg alloy plating layer 3 is improved by forming an alloy phase of Fe, Al, Zn or the like. The alloy phase formed of Fe, Al, and Zn formed at the interface between the steel sheet 2 and the Zn-Mg alloy plating layer 3 is unlikely to affect the corrosion resistance of the Zn-Mg alloy plating layer 3.

For the reasons stated above, even if the plating bath does not contain Fe, the Fe content in the Zn-Mg alloy plating layer 3 may be about 2.0% by mass, but the corrosion resistance of the Zn-Mg alloy plating layer 3 It has little effect. Therefore, the Zn-Mg alloy plating layer 3 may contain 2.0 mass% or less of Fe.

≪ Corrosion product layer (4) >

The Zn-Mg alloy-plated steel sheet 1 is formed by applying on the surface of the Zn-Mg alloy plating layer 3 a magnesium salt of a carboxylic acid having 4 to 20 carbon atoms or a magnesium salt of an alkanesulfonic acid having 4 to 20 carbon atoms And a product layer (4).

The Mg salt of a carboxylic acid or alkanesulfonic acid having 4 to 20 carbon atoms is a stable corrosion product and improves the corrosion resistance of the Zn-Mg alloy coated steel sheet (1).

The alkali metal salt of the carboxylic acid or the alkali metal salt of the alkanesulfonic acid contained in the converted layer 5 is eluted and ionized in the aqueous solution under the chemical treatment process and the corrosive environment. The thus generated ions react with the Mg ions eluted from the Zn-Mg alloy plating layer 3 to produce the Mg salt of the carboxylic acid or the Mg salt of the alkanesulfonic acid contained in the corrosion product layer 4. In order for the Mg salt of the carboxylic acid or the Mg salt of the alkanesulfonic acid to be formed, the alkali metal salt of the carboxylic acid or the alkali metal salt of the alkanesulfonic acid contained in the converted layer 5 is in contact with the Zn-Mg alloy plating layer 3 It needs to be in position.

In order that the alkali metal salt of the carboxylic acid or the alkali metal salt of the alkanesulfonic acid is eluted into the aqueous solution and the Mg salt of the carboxylic acid or the Mg salt of the alkanesulfonic acid is not eluted into the aqueous solution, the alkali metal salt of the carboxylic acid or the alkanesulfonic acid It is necessary that the difference in solubility of the Mg salt is large.

In order to precipitate the Mg salt of the carboxylic acid or alkanesulfonic acid between the conversion treatment layer 5 and the Zn-Mg alloy plating layer 3, the solubility of the Mg salt of the carboxylic acid or alkanesulfonic acid in water is required to be low. Therefore, the number of carbon atoms of the carboxylic acid or alkane sulfonic acid is 4 or more.

To dissolve a carboxylic acid or an alkanesulfonic acid as an ion in an aqueous solution under a corrosive environment, the solubility of the alkali metal salt of a carboxylic acid or an alkanesulfonic acid in water needs to be high. Accordingly, the carbon number of the carboxylic acid or alkanesulfonic acid is 20 or less.

The preferred number of carbon atoms of the carboxylic acid or alkanesulfonic acid is 5 to 20, more preferably 8 to 12.

The carboxylic acid is not particularly limited as long as the number of carbon atoms is 4 to 20, and saturated fatty acids, hydroxycarboxylic acids, benzenecarboxylic acids, dicarboxylic acids, and unsaturated fatty acids can be used. From an economic point of view, it is preferable to use a saturated fatty acid as the carboxylic acid.

Examples of saturated fatty acids include but are not limited to butyric, valeric, caproic, enantic, caprylic, pelargonic, capric, lauric, myristic, pentadecyl, palmitic, margaric, , Arachidic acid, and the like.

Examples of particularly preferable compounds among saturated fatty acids include caprylic acid, pelargonic acid, capric acid and lauric acid having 8 to 12 carbon atoms.

Examples of the hydroxycarboxylic acid include malic acid, citric acid, and tartaric acid. Benzenecarboxylic acids include benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, salicylic acid, cinnamic acid and the like.

Examples of the dicarboxylic acid include fumaric acid, maleic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid and sebacic acid.

Examples of the unsaturated fatty acid include unsaturated fatty acids such as crotonic acid, sorbic acid, myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, benzoic acid, linoleic acid, linolenic acid, arachidonic acid, eicosadienic acid, .

The alkanesulfonic acid is not particularly limited as long as the number of carbon atoms is 4 to 20, and examples thereof include butane sulfonic acid, 2-butanesulfonic acid, pentanesulfonic acid, hexanesulfonic acid, octanesulfonic acid, decanesulfonic acid, dodecanesulfonic acid, tetradecanesulfonic acid, hexadecanesulfonic acid, , Icosanic acid, and the like.

Particularly preferred examples of the alkanesulfonic acid compound include octanesulfonic acid, decanesulfonic acid and dodecanesulfonic acid having 8 to 12 carbon atoms.

≪ Chemical conversion treatment layer (5) >

The Zn-Mg alloy-plated steel sheet 1 has a chemically treated layer 5 containing an alkali metal salt of a carboxylic acid or an alkane sulfonic acid and a film forming component on the surface of the corrosion product layer 4. The chemical conversion treatment layer 5 may contain an inhibitor component and a polyethylene wax if necessary. The converted layer 5 is preferably a chromate-free layer.

<Alkali metal>

The alkali metal of the alkali metal salt of the carboxylic acid or the alkanesulfonic acid contained in the chemical conversion treatment layer 5 is at least one selected from the group consisting of Li, Na, K, Rb and Cs. From the viewpoint of economy, it is preferable that the alkali metal is only Na (the alkali metal salt of carboxylic acid or alkanesulfonic acid is only Na salt of carboxylic acid or alkanesulfonic acid and does not contain alkali metal salt other than Na salt).

The content of the alkali metal salt of the carboxylic acid or alkane sulfonic acid contained in the converted layer 5 is preferably 10 to 1500 mg / m 2 in terms of the amount of Na. When the content of the alkali metal salt of the carboxylic acid or the alkanesulfonic acid is less than 10 mg / m &lt; 2 &gt; in terms of Na amount, the amount of the Mg salt of the carboxylic acid or alkanesulfonic acid contained in the corrosion product layer (4) There is no case. On the other hand, if the content of the alkali metal salt of the carboxylic acid or alkanesulfonic acid exceeds 1,500 mg / m 2 in terms of the Na amount, the uniformity of the converted layer 5 may be deteriorated.

When the solution obtained by immersing the chemical conversion treatment layer 5 in pure water is dried and subjected to qualitative analysis and quantitative analysis by infrared spectroscopy or pyrolysis gas chromatography using the obtained residue, an alkali of a carboxylic acid or alkanesulfonic acid It is possible to identify the carboxylic acid component of the metal salt or the substance of the alkanesulfonic acid. When qualitative analysis and quantitative analysis are carried out by the atomic absorption spectrophotometry using the residue obtained in the same manner as above, the alkali metal component can be identified and the content thereof can be measured. Of the alkali metal components, Na can be qualitatively analyzed and quantitatively analyzed by the uranyl acetic acid salt method.

The converted layer 5 may contain a Mg salt of a carboxylic acid or an alkanesulfonic acid. However, the Mg salt of a carboxylic acid or an alkanesulfonic acid contained in the converted layer 5 hardly contributes to improvement in corrosion resistance.

The carboxylic acid or alkanesulfonic acid in the chemical conversion treatment layer 5 is present only in the form of an alkali metal salt or Mg salt, and the carboxylic acid or alkanesulfonic acid is not present in the chemical conversion treatment layer 5 as a single unit. Likewise, in the chemical conversion treatment layer 5, the alkali metal is not present in the unit.

<Composition of film component>

As the film forming component, a so-called chromated free surface may be used which contains one or both of a resin and a metal compound, irrespective of the kind thereof.

Examples of the resin include a polyurethane resin, an epoxy resin, an acrylic resin and a polyamide resin. The metal compound may include a basic zirconium compound or a silicon compound. Examples of the silicon compound include an organic silicon compound and an inorganic silicon compound.

Hereinafter, examples of desirable film forming components include film forming components (film forming component A) containing at least one of a basic zirconium compound, a phosphoric acid compound and a cobalt compound and an organic acid, a film forming component containing an organic silicon compound and an aqueous urethane resin B), an ethylene-unsaturated carboxylic acid copolymer resin having one or both of a silanol group and an alkoxysilyl group, a silicon oxide particle and an organic titanium compound (film forming component C).

<Coating composition A>

The film forming component A comprises at least one of a basic zirconium compound, a phosphoric acid compound and a cobalt compound and an organic acid.

Examples of the basic zirconium compound include zirconium carbonate compounds having [Zr (CO ₃ ) ₂ (OH) ₂ ] ^2- or [Zr (CO ₃ ) ₂ (OH) ₂ ] ^2- as cations, Ammonium salts, potassium salts, and sodium salts.

Examples of the phosphoric acid compound include phosphoric acid and its ammonium salt such as orthophosphoric acid, pyrophosphoric acid, metaphosphoric acid, polyphosphoric acid, fumaric acid, phosphonic acid, ammonium phosphate, ammonium dihydrogenphosphate, ammonium dihydrogenphosphate, sodium phosphate, .

Examples of the cobalt compound include cobalt carbonate, cobalt nitrate, and cobalt acetate.

Examples of the organic acids include glycolic acid, malic acid, tartaric acid, oxalic acid, citric acid, ascorbic acid, lactic acid, dehydrobenzoic acid, dehydrococcubic acid, gallic acid, tannic acid and pitic acid. Ammonium salts of these organic acids may also be used.

<Coated film component B>

The film forming component B includes an organosilicon compound and an aqueous urethane resin.

Examples of the organosilicon compound include compounds obtained by compounding a silane coupling agent containing one amino group in the molecule and a silane coupling agent containing one glycidyl group in the molecule.

The silane coupling agent containing one amino group in the molecule is not particularly limited, and examples thereof include 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane. Examples of the silane coupling agent containing one glycidyl group in the molecule include 3-glycidoxypropyltrimethoxysilane and 3-glycidoxypropyltriethoxysilane.

The number of functional groups in the organosilicon compound is preferably two or more. When the number of functional groups is one, the adhesiveness with the Zn-Mg alloy plating layer 3, the self-crosslinking property of the organic silicon compound, and the bonding property with the polyether polyurethane resin are lowered, May not be formed.

The number of functional groups of the organosilicon compound can be analyzed by gas chromatography.

The water-based urethane resin is preferably polyether-based. The polyester polyurethane resin sometimes undergoes hydrolysis by an acid or an alkali, and the polycarbonate polyurethane tends to form a hard and brittle coating film, which may adversely affect the adhesion at the time of processing and the corrosion resistance of the processed portion .

The structure of the water-based urethane resin is characterized by the characteristic absorption at 3330 cm ^-1 (NH stretching), 1730 cm ^-1 (C stretching at C = 0), 1530 cm ^-1 (CN), and 1250 cm ^-1 .

&Lt; Film forming component C &

The film forming component C includes an ethylene-unsaturated carboxylic acid copolymer resin, a silicon oxide particle and an organic titanium compound having either or both of a silanol group and an alkoxysilyl group.

The ethylene-unsaturated carboxylic acid copolymer resin having either or both of a silanol group and an alkoxysilyl group is obtained by reacting an aqueous solution in which a copolymer resin of ethylene and an unsaturated carboxylic acid are dispersed with a silane-based compound. Examples of the unsaturated carboxylic acid include, for example, acrylic acid, methacrylic acid, and maleic anhydride.

As the silicon oxide particles, it is preferable to use colloidal silica or fumed silica.

Examples of the organic titanium compound include dipropoxy bis (triethanolaminato) titanium, dipropoxy bis (diethanolaminato) titanium, dibutoxybis (triethanolaminato) titanium, dibutoxy bis (diethanolaminato) (Lactate) titanium monoammonium salt, dihydroxybis (lactate) titanium diammonium salt, propanedioxy titanium bis (acetylacetonato) titanium, dibutoxybis (Ethyl acetoacetate), and oxotitanbis (monoammonium oxalate).

The film forming component C may contain a polyurethane resin having either or both of a silanol group and an alkoxysilyl group in addition to the above-described components. A polyurethane resin having either or both of a silanol group and an alkoxysilyl group can be obtained by reacting a polyurethane prepolymer with an alkoxysilane or polyamine having an active hydrogen group.

Even when the film forming component C contains an unsaturated carboxylic acid, the solution obtained by immersing the converted layer 5 in pure water as described above is dried and the resulting residue is analyzed to find that the carboxylic acid or alkanesulfonic acid Alkali metal salts can be distinguished.

If the chemical conversion treatment layer 5 contains at least one kind selected from the group consisting of fluoride, trivalent chromium and vanadium, since the Mg salt of the carboxylic acid or alkanesulfonic acid is not appropriately precipitated, Is not properly formed. Therefore, it is preferable that the converted layer 5 does not contain fluoride, trivalent chromium, and vanadium.

Further, since the chemical conversion treatment layer 5 does not contain fluoride, trivalent chromium, and vanadium, it is preferable that the film forming component does not contain fluoride, trivalent chromium, and vanadium.

The interface between the Zn-Mg alloy plating layer 3 and the corrosion product layer 4 and the interface between the corrosion product layer 4 and the chemical conversion treatment layer 5 are the SEM- , And can be identified by the contrast of the reflection electron image.

[Manufacturing method of Zn-Mg alloy-plated steel sheet (1)] [

The Zn-Mg alloy plated steel sheet 1 is formed by forming a Zn-Mg alloy plated layer 3 on the surface of the steel sheet 2 by a plating process and then subjecting the surface of the Zn-Mg alloy plated layer 3 to corrosion Is formed by forming the product layer (4) and forming the converted layer (5) on the surface of the corrosion product layer (4).

<Plating Process>

A Zn-Mg alloy plating layer 3 is formed on the surface of the steel sheet 2 by a plating process.

The method of the plating process is not particularly limited, and a known hot-dip coating process can be used. For the addition of Mg and the like to the Zn plating bath, a known method can be used.

<Chemical conversion treatment step>

The corrosion product layer 4 is formed on the surface of the Zn-Mg alloy plating layer 3 and the chemical conversion treatment layer 5 is formed on the surface of the corrosion product layer 4 by the chemical conversion treatment process.

In the chemical conversion treatment step, a solution obtained by dissolving an alkali metal salt of a carboxylic acid or alkanesulfonic acid and a film forming component in water or an organic solvent (hereinafter referred to as a chemical conversion treatment solution) Is applied to the surface of the Zn-Mg alloy plating layer 3 and dried.

The concentration of the alkali metal salt of the carboxylic acid or the alkanesulfonic acid in the chemical conversion solution is not particularly limited, but the alkali metal salt of the carboxylic acid or the alkali metal salt of the alkanesulfonic acid is eluted into the aqueous solution and the Mg salt of the carboxylic acid or the alkane From the viewpoint of preventing the Mg salt of the sulfonic acid from eluting into the aqueous solution, it is preferably 0.1 to 10 mass%.

The coating method of the chemical treatment liquid is not particularly limited, and for example, a spray method, a dipping method, a roll coating method, a showering method, an air knife method, or the like may be employed.

The chemical treatment liquid may contain a surfactant, defoaming agent, lubricant or filler.

The Zn-Mg alloy-plated steel sheet 1 coated with the chemical conversion solution may be heated to 50 to 200 캜 so as to be dried after applying the chemical conversion solution.

Example

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples of the present invention, but the present invention is not limited thereto.

A Zn-Mg alloy plating layer having an adhered amount of 180 g / m &lt; 2 &gt; (90 g / m &lt; 2 &gt; deposition amount per side) was formed on a steel sheet having a thickness of 0.8 mm using a known hot-dip plating method. Further, a corrosion product layer and a chemical conversion treatment layer having a total film thickness of 1.2 占 퐉 were formed on the Zn-Mg alloy plating layer.

The method of forming the corrosion product layer and the chemical conversion treatment layer comprises the steps of: 1% by mass of an alkali metal salt of a carboxylic acid or an alkanesulfonic acid; 20% by mass of a film forming component; and a chemical conversion treatment solution containing water in a bar coating and on a Zn-Mg alloy plating layer Respectively.

The composition of the Zn-Mg alloy plating layer, the alkali metal salt of the carboxylic acid or the alkane sulfonic acid contained in the chemically treated layer, and the film forming component are shown in Tables 1 to 5. These Zn-Mg alloy-plated steel sheets were used as test pieces, and their weathering resistance and corrosion resistance were evaluated as an index of primary resistance. The evaluation results are shown in Tables 6 to 10.

The inventive examples described in Tables 1 and 2 include an alkali metal salt of carboxylic acid in the chemical conversion treatment layer and the inventive examples described in Tables 3 and 4 include alkali metal salts of alkanesulfonic acid in the chemical conversion treatment layer . In the comparative examples described in Table 5, when the chemical conversion treatment layer contains an alkali metal salt of a carboxylic acid, it may contain neither alkali metal salt of alkanesulfonic acid nor both of them.

[Black weathering]

Using a constant temperature and humidity tester, the test piece was allowed to stand for 144 hours under an atmosphere of 80 占 폚 and 85% relative humidity (RH). The color tone of the test piece before and after the standing for 144 hours was measured with a spectroscopic colorimeter to evaluate the black pigmentation. Specifically, the L ^* value indicating the brightness of the CIE colorimetric system (L ^* a ^* b ^* color system) was measured with a spectroscopic colorimetric system, and the difference between the value of L ^* before standing for 144 hours and the value of L ^* That is, (value of L ^* before 144 hours value) was determined in the ΔL ^* (the value of the L ^* value after 144 hours).

On the basis of the value of? L ^*, the black weatherability was evaluated as follows. "Good", "Good" and "Fair".

Very Good: ΔL ^* less than 5

Good: ΔL ^* is more than 5 and less than 10

Fair: ΔL ^* is more than 10 but less than 15

Bad: ΔL ^* exceeded 15

The larger the value of L ^*, the lighter the color, and the smaller the value, the darker the color (black). Based on the time difference 144 of the L ^* value of the test piece before and after the value ΔL ^* While evaluating naeheuk modified, the smaller the value of ΔL ^* value also indicates that after maintaining the brightness before and close value. Further, the larger the value of? L ^*, the lower the brightness (darker) than the pre-set value after the setting.

[Corrosion resistance]

The test pieces were subjected to a salt spray test according to JIS Z 2371 for 240 hours to evaluate the corrosion resistance. Specifically, the corrosion resistance was determined based on the following criteria based on the corrosion area ratio after the salt spray test (the ratio of the corrosion area to the surface area of the test piece). "Good", "Good" and "Fair".

Very Good: Corrosion area rate is 0%

Good: Corrosion area rate is more than 0% and less than 5%

Fair: Corrosion area rate exceeding 5% and below 30%

Bad: corrosion area rate exceeds 30%

Also, in Tables 6 to 10, the comprehensive evaluation based on the above two evaluations is also described. In the overall evaluation, I passed "Very Good", "Good" and "Fair".

As shown in Tables 6 to 9, all of the inventive examples were excellent in weathering resistance and corrosion resistance, and the overall evaluation was acceptable.

On the other hand, in Comparative Examples 1, 2, 5 and 6 shown in Table 10, the content of Mg in the alloy plating layer was out of the range of the present invention, and black weathering, corrosion resistance and comprehensive evaluation were insufficient. In addition, Comparative Examples 1 and 5 are comparative examples in which the content of Mg in the alloy plating layer is large. In Comparative Examples 1 and 5, the corrosion product layer was formed, but the weathering resistance, corrosion resistance and comprehensive evaluation were insufficient. As a reason for this, in Comparative Examples 1 and 5, the formation of the corrosion product layer itself occurs, but it is considered that corrosion of the Mg phase present during plating is rapid, and corrosion can not be suppressed.

In Comparative Examples 3, 4, 7 and 8, the carbon number of the carboxylic acid or alkanesulfonic acid was out of the range of the present invention, and the weathering resistance, corrosion resistance and comprehensive evaluation were insufficient.

Since Comparative Examples 9 to 12 do not contain an alkali metal salt of carboxylic acid or alkanesulfonic acid, the weathering resistance, corrosion resistance and comprehensive evaluation were insufficient.

In Comparative Example 13, since the plating was not performed on the steel sheet, the black marking, the corrosion resistance and the comprehensive evaluation were insufficient. In Comparative Example 13, since the steel sheet is not plated, a source of Mg ions is not present. As a result, Mg salt of carboxylic acid was not formed and no corrosion product layer was formed, so that it was considered that the weathering resistance, corrosion resistance and comprehensive evaluation were insufficient.

Comparative Examples 14 and 15 contain a carboxylic acid or an alkanesulfonic acid, but did not contain an alkali metal salt of a carboxylic acid or an alkanesulfonic acid, so that the weathering resistance, corrosion resistance and comprehensive evaluation were insufficient.

Comparative Example 16 is a comparative example in which the film forming component contains trivalent chromium, but the black marking, the corrosion resistance and the comprehensive evaluation were insufficient.

Comparative Example 17 is a comparative example in which the film forming component contains vanadium, but the black marking, the corrosion resistance and the comprehensive evaluation were insufficient.

Comparative Example 18 is a comparative example in which the film forming component contains fluorine, but the black marking, the corrosion resistance and the comprehensive evaluation are insufficient.

The reason why the film forming component contains trivalent chromium, vanadium or fluorine is not preferable. When the film forming component contains trivalent chromium, vanadium or fluorine, the Mg salt of the carboxylic acid or alkanesulfonic acid is not appropriately precipitated And the corrosion product layer is not formed properly.

According to the above embodiment, it is possible to provide a Zn-Mg alloy plated steel sheet having a chemical conversion treatment layer having excellent primary rust-inhibiting properties.

1: Zn-Mg alloy coated steel sheet
2: Steel plate
3: Zn-Mg alloy plating layer
4: Corrosion product layer
5: Chemical conversion layer

Claims (11)

A steel plate;
A Zn-Mg alloy plating layer formed on the surface of the steel sheet and containing 1.0 to 70.0 mass% of Mg and the balance of Zn and impurities;
A corrosion product layer formed on the surface of the Zn-Mg alloy plating layer and containing either a Mg salt of a carboxylic acid having 4 to 20 carbon atoms and an Mg salt of an alkanesulfonic acid having 4 to 20 carbon atoms;
Wherein the corrosion product layer is formed on the surface of the corrosion product layer and contains an alkali metal salt of the carboxylic acid when the corrosion product layer contains the Mg salt of the carboxylic acid, Containing alkaline metal salt of the alkanesulfonic acid,
And,
Wherein the alkali metal salt of the carboxylic acid or the alkali metal salt of the alkali metal salt of the alkanesulfonic acid contained in the converted layer is at least one selected from the group consisting of Li, Na, K, Rb and Cs
Zn-Mg alloy coated steel sheet. The method according to claim 1, wherein the Zn-Mg alloy plating layer contains 5.0 to 70.0 mass% of Mg
Zn-Mg alloy coated steel sheet. The method according to claim 2, wherein the Zn-Mg alloy plating layer contains 10.0 to 70.0 mass% of Mg
Zn-Mg alloy coated steel sheet. The method according to claim 3, wherein the Zn-Mg alloy plating layer contains 15.0 to 70.0 mass% of Mg
Zn-Mg alloy coated steel sheet. The method according to any one of claims 1 to 4, wherein the Zn-Mg alloy plating layer comprises
0.3 to 25.0 mass% of Al;
0.01 to 5.00 mass% of Si;
1.0 to 5.0% by mass of Ca;
0.1 to 1.5% by mass or less of Ni
And at least one member selected from the group consisting of
Zn-Mg alloy coated steel sheet. 6. The method according to any one of claims 1 to 5, wherein the alkali metal is Na
Zn-Mg alloy coated steel sheet. The method according to claim 6, wherein the content of the alkali metal salt of the carboxylic acid or the alkali metal salt of the alkanesulfonic acid contained in the chemical conversion treatment layer is 10 to 1500 mg / m &lt; 2 &
Zn-Mg alloy coated steel sheet. 8. The method according to any one of claims 1 to 7, wherein the carboxylic acid or alkanesulfonic acid has 5 to 20 carbon atoms
Zn-Mg alloy coated steel sheet. The method according to claim 8, wherein the carboxylic acid or alkanesulfonic acid has 8 to 12 carbon atoms
Zn-Mg alloy coated steel sheet. 10. The process according to any one of claims 1 to 9, wherein the carboxylic acid is a saturated fatty acid
Zn-Mg alloy coated steel sheet. 11. The method according to any one of claims 1 to 10, wherein the converted layer contains fluoride, trivalent chromium and vanadium
Zn-Mg alloy coated steel sheet.

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