| 摘要 |
PURPOSE: A preparation method of chromate solution is provided, and also a method for manufacturing a chromated galvanized steel sheet with excellent corrosion resistance, surface quality and chromium elution resistance by using the chromate solution is provided. CONSTITUTION: The method for preparing a chromate solution comprises preparing a subject solution (a) of which chromium concentration is 5 to 30 g/L, wherein Cr¬3+ ratio in total chromium is 0.4 to 0.6; based on the total amount of chromium in the subject solution, adding colloidal silica 50-80 wt.%, fluoric acid 20-40 wt.%, phosphoric acid 40-80 wt.%, sulfuric acid 5-15 wt.% to the subject solution (b); adding phosphoric acid to 2-10 wt.% of aqueous epoxy-based silane solution; adjusting the above solution at pH 2 to 3; adding 1 to 5 wt.% of chromic acid to the above solution, based on the weight of silane and subsequently heating it for 1 to 2 hours to prepare a hardener solution; mixing 10 to 20 parts by weight of the hardener solution with 100 parts by weight of the subject solution (b). The method for manufacturing chromated galvanized steel sheet using the chromate solution includes step of depositing the chromate solution on a galvanized steel sheet, whose zinc-plated amount is in the range of 60 to 120 g/m¬2, in an amount of 30 to 100 mg/m¬2 based on the adhesion amount of dry coat; and baking the chromated galvanized steel sheet at 40 to 190°C.
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