Zinc-based plated steel sheet having post-treated coating formed thereon and post-treatment method therefor

A method for post-treating a zinc-based plated steel sheet, the method comprising:

• applying a post-treatment coating solution to a zinc-based plating layer of a zinc-based plated steel sheet and drying the applied post-treatment coating solution to form a post-treatment coating on the zinc-based plating layer,
• wherein the post-treatment coating solution includes a metallic oxysalt and an organic compound, the metallic oxysalt includes at least one metal selected from the group consisting of molybdenum (Mo), boron (B), titanium (Ti), and zirconium (Zr), and the organic compound contains a hydroxyl group (—OH), and
• wherein an atomic ratio (O/M) of oxygen (O) to metal (M) included in the post-treatment coating is greater than 2 and smaller than 20,
• the post-treatment coating includes a coating upper portion and a coating lower portion, a thickness of the coating lower portion being ¼ to ¾ of a total thickness of the post-treatment coating,
• an atomic ratio (O/M) of oxygen and metal of the coating upper portion is greater than 5, and
• an atomic ratio (O/M) of oxygen and metal of the coating lower portion is less than 5.