WO2016163461A1 - Zn-Mg合金めっき鋼板 - Google Patents
Zn-Mg合金めっき鋼板 Download PDFInfo
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- WO2016163461A1 WO2016163461A1 PCT/JP2016/061404 JP2016061404W WO2016163461A1 WO 2016163461 A1 WO2016163461 A1 WO 2016163461A1 JP 2016061404 W JP2016061404 W JP 2016061404W WO 2016163461 A1 WO2016163461 A1 WO 2016163461A1
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- C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
- C23C28/02—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material
- C23C28/021—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material including at least one metal alloy layer
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- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
- C23C2/06—Zinc or cadmium or alloys based thereon
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- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
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- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
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- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
- C23C28/02—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material
- C23C28/023—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material only coatings of metal elements only
- C23C28/025—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material only coatings of metal elements only with at least one zinc-based layer
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
- C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
- C23C28/34—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates
Definitions
- the present invention relates to a Zn—Mg alloy plated steel sheet.
- the plating layer formed on the steel surface by plating is a barrier anti-corrosion plating layer type that shields the steel from the outside environment, and a sacrificial anti-corrosion plating layer that protects the steel from corrosion by preferentially corroding the steel. It is roughly divided into two types. Zn has been conventionally used for plating steel, but the plating layer formed by Zn plating is classified as a sacrificial anticorrosion plating layer type.
- the surface of the plated steel sheet (that is, the surface of the plating layer) is subjected to a coating treatment, a chemical conversion treatment, or a lamination process. Rust prevention is improved by applying the surface treatment.
- the chemical conversion treatment is mainly intended to improve the primary rust prevention property that rusts the surface of the plated steel sheet until the plated steel sheet is processed and assembled to become the final product.
- a layer having suitable adhesion to the surface of the plating layer hereinafter referred to as a chemical conversion treatment layer) is formed on the surface of the plating layer.
- Patent Documents 1 to 4 in recent years, in order to improve the corrosion resistance, a Zn—Mg alloy in which a plating layer containing a Zn—Mg alloy is formed on the surface of the steel plate instead of the Zn plated steel plate. Plated steel sheets have been proposed. A Zn—Mg alloy-plated steel sheet has corrosion resistance superior to that of a Zn-plated steel sheet by stabilizing the corrosion product generated in a corrosive environment with Mg.
- Japanese Unexamined Patent Publication No. 2005-146340 Japanese Unexamined Patent Publication No. 2007-23309 Japanese Unexamined Patent Publication No. 2010-248541 Japanese Unexamined Patent Publication No. 2011-218823
- the Zn—Mg alloy-plated steel sheet has excellent corrosion resistance compared to the Zn-plated steel sheet.
- blackening phenomenon the case where the Zn-Mg alloy-plated steel sheet turns black
- chemical conversion treatment the case where the Zn-Mg alloy-plated steel sheet turns black
- swelling occurs in the layer (hereinafter referred to as a swelling formation phenomenon), and a suitable primary rust preventive property may not be obtained.
- the blackening phenomenon is caused by Mg ions eluted from the plating layer forming non-stoichiometric oxides, and the swelling formation phenomenon is caused by the Mg ions eluted from the plating layer continuously producing unstable corrosion. It is thought that it originates in forming a thing.
- the present invention has been made in view of the above circumstances, and an object thereof is to provide a Zn—Mg alloy-plated steel sheet having a chemical conversion treatment layer having excellent primary rust prevention properties.
- the present inventors examined a method for improving the primary rust prevention property by forming a stable corrosion product with Mg ions eluted from the Zn—Mg alloy.
- the present inventors have included a substance having a low solubility of Mg salt and a high solubility of alkali metal salt in the chemical conversion treatment layer, so that Mg eluted from the plating layer in a corrosive environment and the chemical conversion treatment layer It was found that the dissolved substances were combined and the corrosion portion of the plating layer was covered with the formed stable corrosion product, thereby suppressing the blackening phenomenon and the swelling formation phenomenon.
- the present inventors have further studied, and the chemical conversion treatment layer contains an alkali metal salt of a carboxylic acid having 4 to 20 carbon atoms or an alkali metal salt of an alkanesulfonic acid having 4 to 20 carbon atoms.
- the primary rust prevention property of the Zn—Mg alloy plated steel sheet was remarkably improved, and the present invention was completed.
- the present invention adopts the following means in order to solve the above problems and achieve the object.
- a Zn—Mg alloy-plated steel sheet according to one aspect of the present invention is formed on the surface of the steel sheet and the steel sheet, contains 1.0 to 70.0 mass% Mg, and the balance contains Zn and impurities.
- a Zn-Mg alloy plating layer including the 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 formed on the surface of the Zn-Mg alloy plating layer.
- a corrosion product layer containing any one of the above, and an alkali metal salt of the carboxylic acid when formed on the surface of the corrosion product layer and the corrosion product layer contains the Mg salt of the carboxylic acid.
- a chemical conversion treatment layer containing the alkali metal salt of the alkanesulfonic acid is included in the chemical conversion treatment layer
- Alkali metal Li metal salts or alkali metal salts of the alkanesulfonic acid is at least one of Li, Na, K, selected from the group consisting of Rb and Cs.
- the Zn—Mg alloy plating layer contains 0.3 to 25.0 mass% Al and 0 And at least one selected from the group consisting of 0.01 to 5.00% by mass of Si, 1.0 to 5.0% by mass of Ca, and 0.1 to 1.5% by mass or less of Ni. You may employ
- 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 layer is converted to Na.
- a configuration of 10 to 1500 mg / m 2 may be employed.
- the chemical conversion treatment layer may employ a configuration that does not contain fluoride, trivalent chromium, and vanadium. Good.
- FIG. 1 is a schematic diagram showing a layer configuration of a Zn—Mg alloy-plated steel sheet according to an embodiment.
- FIG. 1 is a schematic diagram showing a layer structure of a Zn—Mg alloy plated steel sheet 1.
- the Zn—Mg alloy-plated steel sheet 1 is formed on the surface of the steel sheet 2, the Zn—Mg alloy plating layer 3 formed on the surface of the steel sheet 2 and containing 10 to 70% by mass of Mg, the balance containing Zn and impurities, and Zn— Corrosion product formed on the surface of the Mg alloy plating layer 3 and containing either Mg salt of carboxylic acid having 4 to 20 carbon atoms or Mg salt of alkanesulfonic acid having 4 to 20 carbon atoms
- the corrosion product layer 4 contains an Mg salt of a carboxylic acid
- the corrosion product layer 4 contains an alkali metal salt of a carboxylic acid
- the corrosion product layer 4 contains an alkane sulfone.
- a chemical conversion treatment layer 5 containing an alkali metal salt of alkanesulfonic acid is provided.
- the conventional Zn—Mg alloy-plated steel sheet 1 when the chemical conversion treatment layer 5 was formed on the Zn—Mg alloy plating layer 3, the blackening phenomenon and the swelling formation phenomenon were remarkable.
- the Zn—Mg alloy-plated steel sheet 1 according to the present embodiment suppresses the formation of Mg non-stoichiometric oxides and unstable corrosion products even when the chemical conversion treatment layer 5 is formed. Primary rust resistance is remarkably improved.
- the above-described primary rust prevention effect can be improved by adding an alkali metal salt of a carboxylic acid or alkanesulfonic acid having 4 to 20 carbon atoms to the chemical conversion treatment layer 5.
- an alkali metal salt of a carboxylic acid or alkanesulfonic acid having 4 to 20 carbon atoms to the chemical conversion treatment layer 5.
- Mg ions eluted from the Zn—Mg alloy plating layer 3 and carboxylic acid ions or alkanesulfonic acid ions eluted from the chemical conversion treatment layer 5 are combined to form a stable corrosion product, carboxylic acid.
- An Mg salt of an acid or an alkane sulfonic acid is formed.
- the produced Mg salt of carboxylic acid or Mg salt of alkanesulfonic acid is deposited in a layer form on the Zn—Mg alloy plating layer 3 to form a corrosion product layer 4.
- Carboxylic acid or alkanesulfonic acid having 4 to 20 carbon atoms forms Mg salt by bonding with Mg, and particularly coats the corroded portion. As a result, elution of Mg ions from the Zn—Mg alloy plating layer 3 is suppressed.
- the Zn—Mg alloy plating layer 3 contains a Zn—Mg alloy, and may contain at least one selected from the group consisting of Al, Si, Ca and Ni as necessary. Further, elements such as Y, La, Ce, Ti, Cr, Fe, Co, V, Nb, Cu, Sn, Mn, Sr, Sb, and Pb may be contained in an amount of about 0 to 5% by mass. Below, content of Mg, Al, Si, Ca, Ni is demonstrated.
- the balance other than these alloy elements includes Zn and impurities.
- the impurity is a component mixed due to various factors of the raw material and the manufacturing process, and is a so-called inevitable impurity.
- the balance other than the above alloy elements is preferably composed of Zn and inevitable impurities.
- Mg manganesium
- the Mg content in the Zn—Mg alloy plating layer 3 is 1.0 mass% or more in order to improve sacrificial corrosion resistance.
- the Mg content is preferably 5% by mass or more, more preferably 10% by mass or more, and still more preferably 15% by mass or more.
- the Mg content exceeds 70.0% by mass, the Mg phase is crystallized in the Zn—Mg alloy plating layer 3 and the corrosion resistance is remarkably lowered.
- Mg in the Zn—Mg alloy plating layer 3 reacts with the carboxylic acid or alkanesulfonic acid applied on the surface to generate an Mg salt.
- This Mg salt has a function of further improving the corrosion resistance of the Zn—Mg alloy layer 3 as compared with the case where there is no Mg salt. This is the reason why the corrosion resistance is further improved by the above-mentioned preferable Mg concentration, and there is an effect more than the corrosion resistance obtained by simply increasing the Mg concentration (Tanaka additional note).
- the Zn—Mg alloy plating layer 3 does not contain Mg, the carboxylic acid or alkanesulfonic acid Mg salt described later is not formed, and therefore the corrosion product layer 4 is not formed. Therefore, since suitable corrosion resistance cannot be obtained, it is not preferable.
- Al is an element that improves the corrosion resistance of the planar portion of the Zn—Mg alloy plating layer 3.
- the Zn—Mg alloy plating layer 3 preferably contains 0.30% by mass or more of Al.
- the upper limit is preferably made 25.0% by mass or less.
- the content of Al is more preferably 20.0% by mass or less.
- Si is an element that suppresses growth of the alloy phase formed at the interface between the steel plate 2 and the Zn—Mg alloy plating layer 3 and prevents deterioration of workability. It is preferable to contain 010 mass% or more. If the Si content exceeds 5.0% by mass, bottom dross is likely to be formed in the plating bath and the operability is lowered, so 5.0% by mass or less is preferable.
- ⁇ Ca 1.0 to 5.0% by mass> Ca is added to the Zn—Mg alloy plating layer 3 as necessary to improve the operability of hot dipping.
- an Mg-containing alloy is used as a plating bath.
- Ni is an element that improves wettability during plating.
- the interface between the steel plate 2 and the Zn—Mg alloy plating layer 3 is greater than when the Zn—Mg alloy plating layer 3 is formed on the steel plate 2.
- the formation of Al—Fe-based intermetallic compounds in the vicinity is suppressed, and workability is improved.
- the upper limit of the Ni content of the Zn—Mg alloy plating layer 3 is preferably 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 plating alloy as pre-Ni plating as described above, or may be previously included as a component in the plating alloy.
- an element constituting the steel plate 2 as a base material may be mixed.
- the Zn—Mg alloy plating layer 3 is formed by the hot dipping method, or when heat treatment is performed after the formation of the Zn—Mg alloy plating layer 3, the element is formed at the interface between the steel plate 2 and the Zn—Mg alloy plating layer 3. Interdiffuse. In such a case, the adhesiveness between the steel plate 2 and the Zn—Mg alloy plating layer 3 is improved by forming an alloy phase of Fe, Al, Zn or the like.
- an alloy phase containing Fe, Al, and Zn formed at the interface between the steel plate 2 and the Zn—Mg alloy plating layer 3 is less likely to affect the corrosion resistance of the Zn—Mg alloy plating layer 3.
- the content of Fe in the Zn—Mg alloy plating layer 3 may be about 2.0 mass%.
- the Zn—Mg alloy plating layer 3 may contain 2.0 mass% or less of Fe.
- the Zn—Mg alloy-plated steel sheet 1 contains Mg salt of carboxylic acid having 4 to 20 carbon atoms or Mg salt of alkanesulfonic acid having 4 to 20 carbon atoms on the surface of the Zn—Mg alloy plated layer 3.
- the corrosion product layer 4 has The Mg salt of 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-plated steel sheet 1.
- the alkali metal salt of carboxylic acid or the alkali metal salt of alkanesulfonic acid contained in the chemical conversion treatment layer 5 is ionized by eluting into the aqueous solution under the chemical conversion treatment step and the corrosive environment.
- the ions generated in this manner react with the Mg ions eluted from the Zn—Mg alloy plating layer 3 to generate Mg salt of carboxylic acid or Mg salt of alkanesulfonic acid contained in the corrosion product layer 4. Is done.
- alkali metal salt of carboxylic acid or alkali metal salt of alkanesulfonic acid contained in chemical conversion treatment layer 5 is added to Zn—Mg alloy plating layer 3. It must be in a position where it touches.
- the carboxylic acid In order to prevent the alkali metal salt of carboxylic acid or the alkali metal salt of alkanesulfonic acid from eluting in the aqueous solution and the Mg salt of carboxylic acid or Mg salt of alkanesulfonic acid from eluting into the aqueous solution, the carboxylic acid Alternatively, it is necessary that the difference in solubility between the alkali metal salt of alkanesulfonic acid and the Mg salt is large.
- the solubility of the Mg salt of carboxylic acid or alkanesulfonic acid in water needs to be low. . Therefore, the carbon number of carboxylic acid or alkanesulfonic acid is 4 or more.
- the solubility of the carboxylic acid or alkanesulfonic acid alkali metal salt in water needs to be high. Therefore, carbon number of carboxylic acid or alkanesulfonic acid shall be 20 or less.
- the preferred carbon number of the carboxylic acid or alkanesulfonic acid is 5-20, more preferably 8-12.
- the carboxylic acid is not particularly limited as long as it has 4 to 20 carbon atoms, and saturated fatty acid, hydroxycarboxylic acid, benzenecarboxylic acid, dicarboxylic acid, unsaturated fatty acid and the like can be used. From an economical viewpoint, it is preferable to use a saturated fatty acid as the carboxylic acid.
- saturated fatty acids include butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, arachidic acid, etc. be able to.
- particularly preferred compounds among the saturated fatty acids include caprylic acid, pelargonic acid, capric acid and lauric acid having 8 to 12 carbon atoms.
- Examples of hydroxycarboxylic acid include malic acid, citric acid, tartaric acid and the like.
- benzenecarboxylic acid 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, sebacic acid and the like.
- unsaturated fatty acids include crotonic acid, sorbic acid, myristoleic acid, palmitoleic acid, sapienoic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, linolenic acid, arachidonic acid, eicosadienoic acid, eicosapentaenoic acid, etc. Can be mentioned.
- the alkanesulfonic acid is not particularly limited as long as it has 4 to 20 carbon atoms, butanesulfonic acid, 2-butanesulfonic acid, pentanesulfonic acid, hexanesulfonic acid, octanesulfonic acid, decanesulfonic acid, dodecanesulfonic acid, tetradecane.
- Sulfonic acid, hexadecane sulfonic acid, octadecane sulfonic acid, icosane sulfonic acid and the like can be used.
- Examples of particularly preferable compounds among alkanesulfonic acids include octanesulfonic acid, decanesulfonic acid and dodecanesulfonic acid having 8 to 12 carbon atoms.
- the Zn—Mg alloy-plated steel sheet 1 has a chemical conversion treatment layer 5 made of an alkali metal salt of carboxylic acid or alkanesulfonic 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 polyethylene wax as necessary.
- the chemical conversion treatment layer 5 is preferably so-called chromate-free.
- the alkali metal of the alkali metal salt of carboxylic acid or 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 an economical point of view, the alkali metal is only Na (the alkali metal salt of carboxylic acid or alkanesulfonic acid is only the Na salt of carboxylic acid or alkanesulfonic acid, and does not include alkali metal salts other than Na salt). preferable.
- the content of alkali metal salt of carboxylic acid or alkanesulfonic acid contained in the chemical conversion treatment layer 5 is preferably 10 to 1500 mg / m 2 in terms of Na amount.
- the content of the alkali metal salt of carboxylic acid or alkanesulfonic acid is less than 10 mg / m 2 in terms of Na, the amount of Mg salt of carboxylic acid or alkanesulfonic acid contained in the corrosion product layer 4 is small. May not provide good corrosion resistance.
- the content of the alkali metal salt of carboxylic acid or alkanesulfonic acid exceeds 1500 mg / m 2 in terms of Na amount, the uniformity of the chemical conversion treatment layer 5 may deteriorate.
- carboxylic acid Alternatively, the carboxylic acid component of the alkali metal salt of alkanesulfonic acid or the substance of alkanesulfonic acid can be identified.
- qualitative analysis and quantitative analysis by atomic absorption spectrophotometry can be performed to identify an alkali metal component and measure its content.
- Na can be qualitatively and quantitatively analyzed by the uranyl acetate method.
- the chemical conversion treatment layer 5 may contain Mg salt of carboxylic acid or alkanesulfonic acid
- the Mg salt of carboxylic acid or alkanesulfonic acid contained in the chemical conversion treatment layer 5 hardly contributes to the improvement of corrosion resistance.
- the carboxylic acid or alkanesulfonic acid in the chemical conversion treatment layer 5 exists only in the form of an alkali metal salt or Mg salt, and the carboxylic acid or alkanesulfonic acid does not exist alone in the chemical conversion treatment layer 5.
- the alkali metal does not exist alone.
- ⁇ Film forming component> As long as the film-forming component is so-called chromate-free, regardless of the type, it is possible to use one that includes one or both of a resin and a metal compound.
- the resin include polyurethane resin, epoxy resin, acrylic resin, and polyamide resin.
- the metal compound may include a basic zirconium compound and a silicon compound.
- the silicon compound include organic silicon compounds and inorganic silicon compounds.
- a film-forming component (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, an organic silicon compound and an aqueous urethane are used.
- a film-forming component containing a resin (film-forming component 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 ( The film-forming component C) will be described.
- the film-forming component A contains at least one of a basic zirconium compound, a phosphoric acid compound, and a cobalt compound and an organic acid.
- a 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, and their cations
- phosphoric acid compounds include phosphoric acid and its ammonium salts such as orthophosphoric acid, pyrophosphoric acid, metaphosphoric acid, polyphosphoric acid, phytic acid, phosphonic acid, ammonium phosphate, ammonium dihydrogen phosphate, phosphorus Examples thereof include diammonium oxyhydrogen, sodium phosphate, and potassium phosphate.
- the cobalt compound include cobalt carbonate, cobalt nitrate, and cobalt acetate.
- organic acids examples include glycolic acid, malic acid, tartaric acid, succinic acid, citric acid, ascorbic acid, lactic acid, dehydrobenzoic acid, dehydroascorbic acid, gallic acid, tannic acid, phytic acid, and the like.
- the ammonium salt may be used.
- the film-forming component B contains an organosilicon compound and a water-based urethane resin.
- organosilicon compound include compounds obtained by blending 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 2 or more. When the number of functional groups is one, the adhesion to the Zn—Mg alloy plating layer 3, the self-crosslinking property of the organosilicon compound, and the binding property to the polyether polyurethane resin are lowered, and the chemical conversion treatment layer 5 It may not be formed suitably.
- the number of functional groups of the organosilicon compound can be analyzed by gas chromatography.
- the water-based urethane resin is preferably a polyether system.
- the polyester polyurethane resin may be hydrolyzed by acid or alkali, and the polycarbonate polyurethane is likely to form a hard and brittle film, and may be inferior in adhesion during processing and corrosion resistance of the processed part.
- the film-forming component C includes an ethylene-unsaturated carboxylic acid copolymer resin having one or both of a silanol group and an alkoxysilyl group, silicon oxide particles, and an organic titanium compound.
- An ethylene-unsaturated carboxylic acid copolymer resin having either or both of a silanol group and an alkoxysilyl group includes, for example, an aqueous solution in which a copolymer resin of ethylene and an unsaturated carboxylic acid is dispersed, a silane compound, Is obtained by reacting.
- the unsaturated carboxylic acid include acrylic acid, methacrylic acid, maleic anhydride and the like.
- the silicon oxide particles colloidal silica, fumed silica, or the like is preferably used.
- organic titanium compounds include dipropoxybis (triethanolaminato) titanium, dipropoxybis (diethanolaminato) titanium, dibutoxybis (triethanolaminato) titanium, dibutoxybis (diethanolaminato) titanium, dipropoxybis (acetylacetonato).
- titanium, dibutoxybis (acetylacetonato) titanium dihydroxybis (lactato) titanium monoammonium salt
- dihydroxybis (lactato) titanium diammonium salt propanedioxytitanium bis (ethylacetoacetate), oxotitanium bis (monoammonium o
- the film-forming component C may include a polyurethane resin having one or both of a silanol group and an alkoxysilyl group in addition to the above-described components.
- a polyurethane resin having one or both of a silanol group and an alkoxysilyl group can be obtained by reacting a polyurethane prepolymer with alkoxysilanes and polyamines having an active hydrogen group.
- the film-forming component C contains an unsaturated carboxylic acid, as described above, the solution obtained by immersing the chemical conversion layer 5 in pure water is dried, and the obtained residue is analyzed. For example, discrimination from an alkali metal salt of carboxylic acid or alkanesulfonic acid is possible.
- the chemical conversion treatment layer 5 contains at least one selected from the group consisting of fluoride, trivalent chromium and vanadium
- the Mg salt of carboxylic acid or alkanesulfonic acid does not precipitate properly, and therefore the corrosion product layer 4 is preferably used. Not formed. Therefore, it is preferable that the chemical conversion treatment layer 5 does not contain fluoride, trivalent chromium, and vanadium.
- 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 were obtained by photographing a cross section of the Zn—Mg alloy plated steel sheet 1 with an SEM-reflection electron image. And can be identified by the brightness of the reflected electron image.
- the Zn—Mg alloy plated steel sheet 1 forms a Zn—Mg alloy plating layer 3 on the surface of the steel sheet 2 by a plating process, and forms a corrosion product layer 4 on the surface of the Zn—Mg alloy plating layer 3 by a chemical conversion treatment process. At the same time, the chemical conversion treatment layer 5 is formed on the surface of the corrosion product layer 4.
- a Zn—Mg alloy plating layer 3 is formed on the surface of the steel plate 2 by a plating process.
- the method of the plating step is not particularly limited, and a known hot dipping method can be used. A well-known method can be used also about addition of Mg etc. in Zn plating bath.
- 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.
- a solution in which an alkali metal salt of carboxylic acid or alkanesulfonic acid and the film forming component are dissolved in water or an organic solvent hereinafter referred to as chemical conversion treatment liquid. Is applied to the surface of the Zn—Mg alloy plating layer 3 and dried.
- the concentration of the alkali metal salt of carboxylic acid or alkanesulfonic acid in the chemical conversion treatment liquid is not particularly limited, but the alkali metal salt of carboxylic acid or alkali metal salt of alkanesulfonic acid is eluted in the aqueous solution, and Mg salt of carboxylic acid Or from the viewpoint of preventing the Mg salt of alkanesulfonic acid from eluting into the aqueous solution, the content is preferably 0.1 to 10% by mass.
- the method for applying the chemical conversion liquid is not particularly limited, and for example, a spray method, a dipping method, a roll coating method, a shower ringer method, an air knife method, or the like may be employed.
- the chemical conversion treatment liquid may contain a surfactant, an antifoaming agent, a lubricant, or a filler.
- the Zn—Mg alloy-plated steel sheet 1 coated with the chemical conversion solution may be heated to 50 ° C. to 200 ° C. in order to dry it.
- the formation method of the corrosion product layer and the chemical conversion treatment layer is as follows.
- the chemical conversion treatment solution containing 1% by mass of an alkali metal salt of carboxylic acid or alkanesulfonic acid, 20% by mass of a film-forming component and water is coated with Zn-Mg. It apply
- Tables 1 to 5 show the composition of the Zn—Mg alloy plating layer, the alkali metal salt of carboxylic acid or alkanesulfonic acid contained in the chemical conversion treatment layer, and the film-forming components. Using these Zn—Mg alloy plated steel sheets as test pieces, blackening resistance and corrosion resistance were evaluated as primary rust resistance indicators. The evaluation results are shown in Tables 6 to 10.
- the invention examples described in Tables 1 and 2 include an alkali metal salt of carboxylic acid in the chemical conversion treatment layer
- the invention examples described in Tables 3 and 4 include an alkali metal salt of alkanesulfonic acid in the chemical conversion treatment layer. It is out.
- the chemical conversion treatment layer may contain an alkali metal salt of carboxylic acid, may contain an alkali metal salt of alkanesulfonic acid, or may not contain both of them.
- the above L * represents a brighter color as the value is larger, and represents a darker color (black) as the value is smaller.
- the blackening resistance is evaluated based on ⁇ L * , which is the difference between the L * values of the test pieces before and after 144 hours of standing, but the lightness close to that before standing is maintained as the value of ⁇ L * is smaller. Represents that Further, the larger the value of ⁇ L *, the lower the brightness after standing (becomes darker) than before standing.
- Corrosion resistance was evaluated by performing a salt spray test in accordance with JIS Z 2371 for 240 hours on the test piece. Specifically, the corrosion resistance was determined according to 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). “Very Good”, “Good”, and “Fair” were accepted. Very Good: Corrosion area rate is 0% Good: Corrosion area ratio is more than 0% and less than 5% Fair: Corrosion area ratio is more than 5% and less than 30% Bad: Corrosion area ratio is more than 30%
- Comparative Examples 1, 2, 5 and 6 shown in Table 10 the Mg content of the alloy plating layer was outside the range of the present invention, and blackening resistance, corrosion resistance and comprehensive evaluation were insufficient.
- Comparative examples 1 and 5 are comparative examples in which the alloy plating layer has a high Mg content. In Comparative Examples 1 and 5, the corrosion product layer was formed, but blackening resistance, corrosion resistance, and comprehensive evaluation were insufficient. As a cause of this, although the formation of the corrosion product layer itself occurs in Comparative Examples 1 and 5, it is considered that the corrosion of the Mg phase existing in the plating was fast and the corrosion could not be suppressed.
- Comparative Examples 3, 4, 7 and 8 the carbon number of the carboxylic acid or alkanesulfonic acid was outside the range of the present invention, and the blackening resistance, corrosion resistance and comprehensive evaluation were insufficient. Since Comparative Examples 9 to 12 did not contain an alkali metal salt of carboxylic acid or alkanesulfonic acid, blackening resistance, corrosion resistance, and comprehensive evaluation were insufficient.
- Comparative Example 13 Since the comparative example 13 did not plate on a steel plate, blackening resistance, corrosion resistance, and comprehensive evaluation were inadequate. In Comparative Example 13, since the steel sheet is not plated, there is no Mg ion supply source. Therefore, since Mg salt of carboxylic acid was not formed and the corrosion product layer was not formed, it is considered that blackening resistance, corrosion resistance and comprehensive evaluation were insufficient. Comparative Examples 14 and 15 contained carboxylic acid or alkanesulfonic acid but did not contain an alkali metal salt of carboxylic acid or alkanesulfonic acid, and thus blackening 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 blackening resistance, corrosion resistance, and comprehensive evaluation were insufficient.
- Comparative Example 17 is a comparative example in which the film forming component contains vanadium, but the blackening resistance, corrosion resistance, and comprehensive evaluation were insufficient.
- Comparative Example 18 is a comparative example in which the film-forming component contains fluorine, but the blackening resistance, corrosion resistance, and comprehensive evaluation were insufficient.
- the film-forming component contains trivalent chromium, vanadium or fluorine
- the Mg salt of carboxylic acid or alkanesulfonic acid is This is probably because the corrosion product layer is not properly formed and the corrosion product layer is not suitably formed.
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Abstract
Description
本願は、2015年4月7日に、日本に出願された特願2015-78585号に基づき優先権を主張し、その内容をここに援用する。
なお、黒変現象は、めっき層から溶出したMgイオンが不定比酸化物を形成することに起因しており、膨れ形成現象は、めっき層から溶出したMgイオンが継続して不安定な腐食生成物を形成することに起因していると考えられる。
本発明は、上記課題を解決して、係る目的を達成するために以下の手段を採用する
(Zn-Mg合金めっき鋼板1)
図1は、Zn-Mg合金めっき鋼板1の層構成を示す概要図である。Zn-Mg合金めっき鋼板1は、鋼板2と、鋼板2の表面に形成され、10~70質量%のMgを含有し、残部がZn及び不純物を含むZn-Mg合金めっき層3と、Zn-Mg合金めっき層3の表面に形成され、炭素数が4~20であるカルボン酸のMg塩と炭素数が4~20であるアルカンスルホン酸のMg塩とのいずれか一方を含有する腐食生成物層4と、腐食生成物層4の表面に形成され、腐食生成物層4がカルボン酸のMg塩を含有する場合にはカルボン酸のアルカリ金属塩を含有し、腐食生成物層4がアルカンスルホン酸のMg塩を含有する場合にはアルカンスルホン酸のアルカリ金属塩を含有する化成処理層5と、を備える。
従来のZn-Mg合金めっき鋼板1は、Zn-Mg合金めっき層3上に化成処理層5を形成したときに黒変現象や膨れ形成現象が顕著であった。しかしながら、本実施形態に係るZn-Mg合金めっき鋼板1は、化成処理層5を形成した場合であっても、Mgの不定比酸化物や不安定な腐食生成物の形成を抑制することにより、一次防錆性が著しく向上している。
Zn-Mg合金めっき層3は、Zn-Mg合金を含有し、必要に応じて、Al、Si、Ca及びNiからなる群から選ばれる少なくとも1種以上を含有してもよい。更に、Y、La、Ce、Ti、Cr、Fe、Co、V、Nb、Cu、Sn、Mn、Sr、Sb、Pb等の元素を0~5質量%程度含有してもよい。
以下では、Mg、Al、Si、Ca、Niの含有量について説明する。なお、これらの合金元素以外の残部は、Zn及び不純物を含む。ここで、不純物とは、原料や製造工程の種々の要因によって混入する成分であり、いわゆる不可避的不純物である。上記の合金元素以外の残部はZn及び不可避的不純物からなることが好ましい。
Mg(マグネシウム)は、Znと共にZn-Mg合金めっき層3を構成する主要な元素である。Zn-Mg合金めっき層3におけるMgの含有量は、犠牲防食性を向上させるために、1.0質量%以上とする。好ましくはMgの含有量を5質量%以上、より好ましくは10質量%以上、さらに好ましくは15質量%以上とする。一方、Mgの含有量が70.0質量%を超えると、Zn-Mg合金めっき層3中でMg相が晶出し、耐食性が著しく低下するため、好ましくない。
後述するように、Zn-Mg合金めっき層3中のMgは、表面に塗布したカルボン酸又はアルカンスルホン酸と反応してMg塩を生成する。このMg塩は、Mg塩が無い時に比べてZn-Mg合金層3の耐食性を、更に向上させる作用を有する。上記の好ましいMg濃度により耐食性が更に向上するのは、この理由であり、単にMg濃度を増加して得られる耐食性より以上の効果を奏する(田中追記)。
Zn-Mg合金めっき層3がMgを含有しない場合には、後述するカルボン酸又はアルカンスルホン酸のMg塩が形成されないため、腐食生成物層4が形成されない。そのため、好適な耐食性が得られないため、好ましくない。
Alは、Zn-Mg合金めっき層3の平面部の耐食性を向上させる元素である。この効果を得るために、Zn-Mg合金めっき層3に0.30質量%以上のAlを含有させることが好ましい。一方、Alの含有量が25.0質量%を超えると、赤錆が発生し易くなり耐食性が低下することがあるため、上限を25.0質量%以下とすることが好ましい。Zn-Mg合金めっき層3に対する化成処理層5の密着性を考慮すると、Alの含有量は20.0質量%以下がより好ましい。
Siは、鋼板2とZn-Mg合金めっき層3との界面に形成される合金相の成長を抑制するとともに、加工性の低下を防止する元素であり、Zn-Mg合金めっき層3に0.010質量%以上含有させることが好ましい。Siの含有量が5.0質量%を超えると、めっき浴中にボトムドロスが形成されやすくなり、操業性が低下するため、5.0質量%以下が好ましい。
Caは、溶融めっきの操業性を改善するために、必要に応じてZn-Mg合金めっき層3に添加される。本実施形態に係るZn-Mg合金めっき鋼板1を製造する際には、Mg含有合金をめっき浴として用いる。溶融状態のMg含有合金が表面に好適な酸化被膜を形成するために、Mgの酸化の防止に有効な元素であるCaを1.0質量%以上添加することが好ましい。Caは、含有量が多い場合には耐食性を劣化させる場合があるため、Zn-Mg合金めっき層3におけるCaの含有量の上限を5.0質量%とすることが好ましい。
Niは、めっき時の濡れ性を向上させる元素である。予めNiをめっきした鋼板2にZn-Mg合金めっき層3を形成すると、鋼板2上にZn-Mg合金めっき層3を形成した場合よりも、鋼板2とZn-Mg合金めっき層3との界面付近におけるAl-Fe系金属間化合物の形成が抑制され、加工性が向上する。一方、Niの含有量が多いと、耐食性が劣化する場合があるため、Zn-Mg合金めっき層3のNiの含有量の上限を、1.50%とすることが好ましい。Zn-Mg合金めっき層3のNiの含有量は、0.10質量%以上が好ましい。
尚、Niは上記の様にプレNiメッキとしてメッキ合金中に含まれる様にしても良いし、あらかじめメッキ合金中の一成分として含ませておいても良い。
上述の理由から、めっき浴がFeを含まない場合であっても、Zn-Mg合金めっき層3中のFeの含有量が2.0質量%程度になる場合があるが、Zn-Mg合金めっき層3の耐食性にほとんど影響を与えない。よって、Zn-Mg合金めっき層3は、2.0質量%以下のFeを含有してもよい。
Zn-Mg合金めっき鋼板1は、Zn-Mg合金めっき層3の表面に、炭素数が4~20であるカルボン酸のMg塩又は炭素数が4~20であるアルカンスルホン酸のMg塩を含有する腐食生成物層4を有する。
炭素数が4~20であるカルボン酸又はアルカンスルホン酸のMg塩は、安定した腐食生成物であり、Zn-Mg合金めっき鋼板1の耐食性を向上させる。
カルボン酸のアルカリ金属塩又はアルカンスルホン酸のアルカリ金属塩が水溶液中に溶出し、かつ、カルボン酸のMg塩又はアルカンスルホン酸のMg塩が水溶液中に溶出しないようにするためには、カルボン酸又はアルカンスルホン酸のアルカリ金属塩とMg塩との溶解度の差が大きいことが必要である。
腐食環境下で水溶液中にカルボン酸又はアルカンスルホン酸がイオンとして溶出するには、カルボン酸又はアルカンスルホン酸のアルカリ金属塩の水に対する溶解度が大きい必要がある。そのため、カルボン酸又はアルカンスルホン酸の炭素数を20以下とする。
なお、カルボン酸又はアルカンスルホン酸の好ましい炭素数は、5~20であり、より好ましくは8~12である。
飽和脂肪酸の例としては、酪酸、吉草酸、カプロン酸、エナント酸、カプリル酸、ペラルゴン酸、カプリン酸、ラウリン酸、ミリスチン酸、ペンタデシル酸、パルミチン酸、マルガリン酸、ステアリン酸、アラキジン酸などを挙げることができる。
飽和脂肪酸の中でも特に好ましい化合物の例としては、炭素数が8~12であるカプリル酸、ペラルゴン酸、カプリン酸及びラウリン酸が挙げられる。
ジカルボン酸の例としては、フマル酸、マレイン酸、コハク酸、グルタル酸、アジピン酸、ピメリン酸、スベリン酸、アゼライン酸、セバシン酸などを挙げることができる。
不飽和脂肪酸の例としては、クロトン酸、ソルビン酸、ミリストレイン酸、パルミトレイン酸、サピエン酸、オレイン酸、エライジン酸、バクセン酸、リノール酸、リノレン酸、アラキドン酸、エイコサジエン酸、エイコサペンタエン酸などを挙げることができる。
アルカンスルホン酸の中でも特に好ましい化合物の例としては、炭素数が8~12であるオクタンスルホン酸、デカンスルホン酸及びドデカンスルホン酸が挙げられる。
Zn-Mg合金めっき鋼板1は、腐食生成物層4の表面に、カルボン酸又はアルカンスルホン酸のアルカリ金属塩と造膜成分とからなる化成処理層5を有する。化成処理層5には、必要に応じて、インヒビター成分と、ポリエチレンワックスと、を含有してもよい。化成処理層5は、いわゆるクロメートフリーであることが好ましい。
化成処理層5に含まれるカルボン酸又はアルカンスルホン酸のアルカリ金属塩のアルカリ金属は、Li、Na、K、Rb及びCsからなる群から選ばれる少なくとも1種である。経済的観点から、アルカリ金属がNaのみである(カルボン酸又はアルカンスルホン酸のアルカリ金属塩がカルボン酸又はアルカンスルホン酸のNa塩のみであり、Na塩以外のアルカリ金属塩を含まない)ことが好ましい。
また、化成処理層5中のカルボン酸又はアルカンスルホン酸は、アルカリ金属塩又はMg塩の態様としてのみ存在し、カルボン酸又はアルカンスルホン酸は化成処理層5において単体では存在しない。同様に、化成処理層5において、アルカリ金属は単体では存在しない。
造膜成分は、いわゆるクロメートフリーであれば、特に種類を問わず、樹脂と金属化合物との一方又は両方を含むものを使用することができる、
樹脂の例としては、ポリウレタン樹脂、エポキシ樹脂、アクリル樹脂、ポリアミド樹脂が挙げられる。金属化合物は、塩基性ジルコニウム化合物やケイ素化合物などを含んでもよい。ケイ素化合物の例としては、有機ケイ素化合物、無機ケイ素化合物が挙げられる。
造膜成分Aは、塩基性ジルコニウム化合物、りん酸化合物及びコバルト化合物のうちの少なくとも一つと有機酸とを含む。
塩基性ジルコニウム化合物の例としては、カチオンとして[Zr(CO3)2(OH)2]2-や[Zr(CO3)2(OH)2]2-を有する炭酸ジルコニウム化合物や、これらのカチオンを含有するアンモニウム塩、カリウム塩、ナトリウム塩などが挙げられる。
りん酸化合物の例としては、りん酸やそのアンモニウム塩、例えば、オルトりん酸、ピロりん酸、メタりん酸、ポリりん酸、フィチン酸、ホスホン酸、りん酸アンモニウム、りん酸二水素アンモニウム、りん酸水素二アンモニウム、りん酸ナトリウム、りん酸カリウムなどが挙げられる。
コバルト化合物の例としては、炭酸コバルト、硝酸コバルト、酢酸コバルトなどが挙げられる。
造膜成分Bは、有機ケイ素化合物と水系ウレタン樹脂とを含む。
有機ケイ素化合物の例としては、分子中にアミノ基を1つ含有するシランカップリング剤と、分子中にグリシジル基を1つ含有するシランカップリング剤とを配合して得られる化合物が挙げられる。
分子中にアミノ基を1つ含有するシランカップリング剤としては、特に限定するものではないが、3-アミノプロピルトリエトキシシラン、3-アミノプロピルトリメトキシシランなどを例示することができる。分子中にグリシジル基を1つ含有するシランカップリング剤としては、3-グリシドキシプロピルトリメトキシシラン、3-グリシドキシプロピルトリエトキシシランなどを例示することができる。
有機ケイ素化合物の官能基の数は、ガスクロマトグラフ法により分析することができる。
造膜成分Cは、シラノール基とアルコキシシリル基とのいずれか一方又は両方を有するエチレン-不飽和カルボン酸共重合樹脂、酸化ケイ素粒子及び有機チタン化合物を含む。
シラノール基とアルコキシシリル基とのいずれか一方又は両方を有するエチレン-不飽和カルボン酸共重合樹脂は、例えば、エチレンと不飽和カルボン酸との共重合樹脂を分散させた水溶液と、シラン系化合物とを反応させることによって得られる。不飽和カルボン酸の例としては、例えば、アクリル酸、メタクリル酸、無水マレイン酸等を挙げることができる。
酸化ケイ素粒子としては、コロイダルシリカやヒュームドシリカ等を用いることが好ましい。
また、化成処理層5がフッ化物、3価クロム及びバナジウムを含有しないために、造膜成分もフッ化物、3価クロム及びバナジウムを含有しないことが好ましい。
Zn-Mg合金めっき鋼板1は、めっき工程により鋼板2の表面にZn-Mg合金めっき層3を形成し、化成処理工程によりZn-Mg合金めっき層3の表面に腐食生成物層4を形成するとともに腐食生成物層4の表面に化成処理層5を形成することで製造される。
めっき工程により、鋼板2の表面にZn-Mg合金めっき層3を形成する。
めっき工程の方法は特に限定されず、公知の溶融めっき法を用いることができる。Znめっき浴中へのMg等の添加についても、公知の方法を用いることができる。
化成処理工程により、Zn-Mg合金めっき層3の表面に腐食生成物層4を形成するとともに、腐食生成物層4の表面に化成処理層5を形成する。
化成処理工程では、化成処理層5の造膜成分の種類を問わず、カルボン酸又はアルカンスルホン酸のアルカリ金属塩と造膜成分とを水や有機溶剤に溶解させた溶液(以下、化成処理液と呼称する)をZn-Mg合金めっき層3の表面に塗布し、乾燥させる。
化成処理液におけるカルボン酸又はアルカンスルホン酸のアルカリ金属塩の濃度は特に限定されないが、カルボン酸のアルカリ金属塩又はアルカンスルホン酸のアルカリ金属塩が水溶液中に溶出し、かつ、カルボン酸のMg塩又はアルカンスルホン酸のMg塩が水溶液中に溶出しないようにする観点から、0.1~10質量%が好ましい。
化成処理液は、界面活性剤、消泡剤、潤滑剤又は充填剤を含んでもよい。
化成処理液を塗布した後、乾燥させるために、化成処理液が塗布されたZn-Mg合金めっき鋼板1を50℃~200℃に加熱してもよい。
腐食生成物層及び化成処理層の形成方法は、カルボン酸又はアルカンスルホン酸のアルカリ金属塩を1質量%、造膜成分を20質量%及び水を含有する化成処理液をバー塗装でZn-Mg合金めっき層上に塗布した。
Zn-Mg合金めっき層の組成、化成処理層に含まれるカルボン酸又はアルカンスルホン酸のアルカリ金属塩、造膜成分を表1~5に示す。これらのZn-Mg合金めっき鋼板を試験片として用いて、一次耐錆性の指標として耐黒変性及び耐食性を評価した。評価結果を表6~10に示す。
恒温恒湿試験機を使用して、80℃及び相対湿度(RH)85%の雰囲気下で試験片を144時間静置した。144時間静置前後の試験片の色調を分光測色計で測定し、耐黒変性を評価した。具体的には、分光測色計でCIE表色系(L*a*b*表色系)の明度を表すL*値を測定し、144時間静置前のL*の値と144時間静置後のL*の値との差分(つまり、(144時間静置前のL*の値)-(144時間静置後のL*の値))である△L*を求めた。
ΔL*の値に基づき、以下のように耐黒変性を評価した。「Very Good」、「Good」、「Fair」を合格とした。
Very Good:△L*が5以下
Good:△L*が5超10以下
Fair:△L*が10超15以下
Bad:△L*が15超
試験片に対し、JIS Z 2371に準拠する塩水噴霧試験を240時間実施することにより、耐食性を評価した。具体的には、耐食性は、塩水噴霧試験後の腐食面積率(試験片の表面積に対する腐食面積の割合)にて以下の基準で判定した。「Very Good」、「Good」、「Fair」を合格とした。
Very Good:腐食面積率が0%
Good:腐食面積率が0%超5%以下
Fair:腐食面積率が5%超30%以下
Bad:腐食面積率が30%超
比較例3、4、7及び8は、カルボン酸又はアルカンスルホン酸の炭素数が本発明の範囲外であり、耐黒変性、耐食性及び総合評価が不十分であった。
比較例9~12は、カルボン酸又はアルカンスルホン酸のアルカリ金属塩を含まないため、耐黒変性、耐食性及び総合評価が不十分であった。
比較例14及び15は、カルボン酸又はアルカンスルホン酸を含んでいるが、カルボン酸又はアルカンスルホン酸のアルカリ金属塩を含んでいないため、耐黒変性、耐食性及び総合評価が不十分であった。
比較例17は、造膜成分がバナジウムを含有する比較例であるが、耐黒変性、耐食性及び総合評価が不十分であった。
比較例18は、造膜成分がフッ素を含有する比較例であるが、耐黒変性、耐食性及び総合評価が不十分であった。
造膜成分が3価クロム、バナジウム又はフッ素を含有すると好ましくない理由としては、造膜成分が3価クロム、バナジウム又はフッ素を含有している場合には、カルボン酸又はアルカンスルホン酸のMg塩が適切に沈殿せず、腐食生成物層が好適に形成されないためであると考えられる。
2 鋼板
3 Zn-Mg合金めっき層
4 腐食生成物層
5 化成処理層
Claims (11)
- 鋼板と;
前記鋼板の表面に形成され、1.0~70.0質量%のMgを含有し、残部がZn及び不純物を含むZn-Mg合金めっき層と;
前記Zn-Mg合金めっき層の表面に形成され、炭素数が4~20であるカルボン酸のMg塩と炭素数が4~20であるアルカンスルホン酸のMg塩とのいずれか一方を含有する腐食生成物層と;
前記腐食生成物層の表面に形成され、前記腐食生成物層が前記カルボン酸のMg塩を含有する場合には前記カルボン酸のアルカリ金属塩を含有し、前記腐食生成物層が前記アルカンスルホン酸のMg塩を含有する場合には前記アルカンスルホン酸のアルカリ金属塩を含有する化成処理層と;
を備え、
前記化成処理層に含まれる前記カルボン酸のアルカリ金属塩又は前記アルカンスルホン酸のアルカリ金属塩のアルカリ金属が、Li、Na、K、Rb及びCsからなる群より選ばれる少なくとも1種である、
ことを特徴とする、Zn-Mg合金めっき鋼板。 - 前記Zn-Mg合金めっき層が、5.0~70.0質量%のMgを含有する
ことを特徴とする、請求項1に記載のZn-Mg合金めっき鋼板。 - 前記Zn-Mg合金めっき層が、10.0~70.0質量%のMgを含有する
ことを特徴とする、請求項2に記載のZn-Mg合金めっき鋼板。 - 前記Zn-Mg合金めっき層が、15.0~70.0質量%のMgを含有する
ことを特徴とする、請求項3に記載のZn-Mg合金めっき鋼板。 - 前記Zn-Mg合金めっき層が、
0.3~25.0質量%のAlと;
0.01~5.00質量%のSiと;
1.0~5.0質量%のCaと;
0.1~1.5質量%以下のNiと;
からなる群より選ばれる少なくとも1種を更に含む
ことを特徴とする、請求項1~4の何れか1項に記載のZn-Mg合金めっき鋼板。 - 前記アルカリ金属が、Naである
ことを特徴とする、請求項1~5の何れか1項に記載のZn-Mg合金めっき鋼板。 - 前記化成処理層に含まれる前記カルボン酸のアルカリ金属塩又は前記アルカンスルホン酸のアルカリ金属塩の含有量が、Naに換算して10~1500mg/m2である
ことを特徴とする、請求項6に記載のZn-Mg合金めっき鋼板。 - 前記カルボン酸又は前記アルカンスルホン酸の炭素数が、5~20である
ことを特徴とする、請求項1~7の何れか1項に記載のZn-Mg合金めっき鋼板。 - 前記カルボン酸又は前記アルカンスルホン酸の炭素数が、8~12である
ことを特徴とする、請求項8に記載のZn-Mg合金めっき鋼板。 - 前記カルボン酸が、飽和脂肪酸である
ことを特徴とする、請求項1~9の何れか1項に記載のZn-Mg合金めっき鋼板。 - 前記化成処理層が、フッ化物、3価クロム及びバナジウムを含有しない
ことを特徴とする、請求項1~10の何れか1項に記載のZn-Mg合金めっき鋼板。
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