A surface treatment solution composition for forming an inorganic film, comprising: 10 to 30% by weight of a trivalent chromium compound containing chromium phosphate (A) and chromium nitrate (B) and satisfying a content ratio A/(A+B) of 0.3 to 0.6; 5 to 50% by weight of a silane compound; 0.2 to 3% by weight of a vanadium-based rust-inhibiting and corrosion-resisting agent; 0.5 to 5% by weight of a cobalt-based rust-inhibiting and corrosion-resisting agent; and 12 to 84.3% by weight of water, an alloyed hot-dip galvanized steel sheet surface-treated using the composition, and a method for manufacturing the alloyed hot-dip galvanized steel sheet, are provided, and the surface treatment solution composition containing the trivalent chromium compound has an excellent effect on corrosion resistance, blackening resistance, fuel resistance, weldability, and alkali resistance.

The invention relates to a method for producing a silane-modified silicate. In order to obtain optimal corrosion protection properties, a silane compound according to the invention is at least partially hydrolyzed and/or condensed in the presence of a silicate compound at a pH value greater than or equal to 8 and then a pH value less than or equal to 7 is set by adding acid. The invention further relates to an aqueous acidic passivation composition for metal substrate coated with the passivation composition.

The invention relates to a method for producing a silane-modified silicate. In order to obtain optimal corrosion protection properties, a silane compound according to the invention is at least partially hydrolyzed and/or condensed in the presence of a silicate compound at a pH value greater than or equal to 8 and then a pH value less than or equal to 7 is set by adding acid. The invention further relates to an aqueous acidic passivation composition for metal substrate coated with the passivation composition.

A method includes providing a workpiece with at least one surface having an anodized aluminum coating and a trivalent chromium sealant. The at least one surface of the workpiece is submerged in a post-treatment sealant solution for 0.5 to 20 minutes. The sealant composition consists essentially of a corrosion inhibitor formulation, a water soluble polymer, an organic complexing agent, and an oxidant. The corrosion inhibitor formulation is formulated from at least one anodic corrosion inhibitor compound, at least one cathodic corrosion inhibitor compound, or a combination thereof. A concentration of each of the corrosion inhibitor formulation, the water soluble polymer, the organic complexing agent, and the oxidant is each in a range of 1-50 mM.

A method includes providing a workpiece with at least one surface having an anodized aluminum coating and a trivalent chromium sealant. The at least one surface of the workpiece is submerged in a post-treatment sealant solution for 0.5 to 20 minutes. The sealant composition consists essentially of a corrosion inhibitor formulation, a water soluble polymer, an organic complexing agent, and an oxidant. The corrosion inhibitor formulation is formulated from at least one anodic corrosion inhibitor compound, at least one cathodic corrosion inhibitor compound, or a combination thereof. A concentration of each of the corrosion inhibitor formulation, the water soluble polymer, the organic complexing agent, and the oxidant is each in a range of 1-50 mM.

A steel sheet for a fuel tank according to the present invention includes: a ZnNi alloy plated layer placed on one surface or each of both surfaces of a base metal; and a chromate-free chemical conversion coating film which is placed over the ZnNi alloy plated layer. The ZnNi alloy plated layer has a crack starting from an interface with the chromate-free chemical conversion coating film and reaching an interface with the steel sheet, the chromate-free chemical conversion coating film consists of an organosilicon compound consisting of a condensation polymer of a silane coupling agent, a phosphoric acid compound and/or a phosphonic acid compound, a vanadium compound, and a titanium compound and/or a zirconium compound, and a concentration of a total of amounts in terms of metal, per surface, of the phosphoric acid compound and/or the phosphonic acid compound+the vanadium compound+the titanium compound and/or the zirconium compound, is 5 mass % to 20 mass %.

A steel sheet for a fuel tank according to the present invention includes: a ZnNi alloy plated layer placed on one surface or each of both surfaces of a base metal; and a chromate-free chemical conversion coating film which is placed over the ZnNi alloy plated layer. The ZnNi alloy plated layer has a crack starting from an interface with the chromate-free chemical conversion coating film and reaching an interface with the steel sheet, the chromate-free chemical conversion coating film consists of an organosilicon compound consisting of a condensation polymer of a silane coupling agent, a phosphoric acid compound and/or a phosphonic acid compound, a vanadium compound, and a titanium compound and/or a zirconium compound, and a concentration of a total of amounts in terms of metal, per surface, of the phosphoric acid compound and/or the phosphonic acid compound+the vanadium compound+the titanium compound and/or the zirconium compound, is 5 mass % to 20 mass %.

A method for applying an anti-corrosion coating to a substrate includes: applying an anti-corrosion composition; and applying a dye which exhibits fluorescence when exposed to ultraviolet radiation.

A steel sheet for a fuel tank includes: a ZnNi alloy plated layer which is placed on one surface or each of both surfaces of a base metal and formed on at least one surface; and an inorganic chromate-free chemical conversion coating film which is placed over the ZnNi alloy plated layer. The ZnNi alloy plated layer has a crack starting from an interface between the ZnNi alloy plated layer and the inorganic chromate-free chemical conversion coating film and reaching an interface between the ZnNi alloy plated layer and the steel sheet, and a water contact angle on a surface of the inorganic chromate-free chemical conversion coating film is more than or equal to 50 degrees.

A steel sheet for a fuel tank includes: a ZnNi alloy plated layer which is placed on one surface or each of both surfaces of a base metal and formed on at least one surface; and an inorganic chromate-free chemical conversion coating film which is placed over the ZnNi alloy plated layer. The ZnNi alloy plated layer has a crack starting from an interface between the ZnNi alloy plated layer and the inorganic chromate-free chemical conversion coating film and reaching an interface between the ZnNi alloy plated layer and the steel sheet, and a water contact angle on a surface of the inorganic chromate-free chemical conversion coating film is more than or equal to 50 degrees.