Hot-dip Zn-Al alloy coated steel sheet and process for the production thereof

Abstract

A hot-dip Zn-Al alloy coated steel sheet exhibiting a beautiful coating appearance with metallic luster, in which no spangle or very fine spangles are formed, and having excellent blackening resistance and a method for manufacturing the hot-dip Zn-Al alloy coated steel sheet are provided. The hot-dip Zn-Al alloy coated steel sheet includes a hot-dip Zn-Al alloy coating layer containing 1.0 to 10 percent by mass of Al, 0.2 to 1.0 percent by mass of Mg, 0.005 to 0.1 percent by mass of Ni, and the balance being Zn and incidental impurities on at least one surface of a steel sheet. The manufacturing method includes the steps of dipping the steel sheet into a hot-dip Zn-Al alloy coating bath and pulling up and cooling the steel sheet, wherein the steel sheet pulled up from the coating bath is cooled to 250°C at a cooling rate of 1°C to 15°C / sec.

Description

[0001] This application is an invention whose application number is 200780034445.X (international application number is PCT / JP2007 / 072140), the application date is November 8, 2007, and the invention name is "hot-dip Zn-Al alloy steel plate and its manufacturing method" A divisional application of a patent application. technical field [0002] The present invention relates to a hot-dip Zn-Al alloy steel sheet excellent in plating appearance and blackening resistance used in the fields of construction, civil engineering, and home appliances, and a manufacturing method thereof. Background technique [0003] Conventional hot-dip Zn-Al-based alloy steel sheets are widely used in the fields of automobiles, construction, civil engineering, home appliances, and the like as so-called precoated steel sheets on which a coating is applied to the surface. As the hot-dip Zn-Al alloy steel sheet, mainly used is a hot-dip Zn steel sheet (hereinafter referred to as GI) whose Al content in t...

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Problems solved by technology

[0019] In the plated steel sheet of Patent Document 1, assuming that the blackening resistance can be improved to some extent, the appearance of the plated steel plate is likely to be poor due to the decrease of the color tone and the adhesion of dross, and cracks are easily formed on the plated layer, so the workability is also likely to be deteriorated. Difference

In addition, when there is too much Mg, the blackening resistance is also poor.

[0020] The chromate-treated plated steel sheets of Patent Documents 2 and 3 have insufficient effect of improving the blackening resistance and form spangles similar to ordinary GF, so that the appearance of plated steel sheets and painted steel sheets is likely to be poor.

In addition, in Patent Document 2, chromate treatment using a specific chromate treatment solution must be performed

[0021] In the plated steel sheet of Patent Document 4, any one of problems such as reduction in blackening resistance, deterioration in color tone, poor appearance due to adhesion of dross, and poor appearance due to formation of spangles occurs.

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