Zinc-based plated steel sheet having post-treated coating formed thereon
Provided is a zinc-based plated steel sheet having a post-treated coating filmed thereon including: a steel sheet; a zinc plated layer formed on the steel sheet; and a post-treated coating formed on the plated layer, wherein the atomic ratio (O/M) of oxygen (O) to metals (M) contained in the post-treated coating is greater than 2 and less than 20, and a method for post-treating a zinc-based plated steel sheet. According to this, the zinc-based plated steel sheet having the post-treated coating formed thereon has the effects excellent in lubricity, weldability, adhesiveness, film-removing property and paintability. As the method of post-treating a zinc-based plated steel sheet of the present invention employs a simple coating method irrespective of the kind of plating layer, the process is simple and economical and the process operation cost is low.
1. A zinc-based plated steel sheet having a post-treatment coating, the zinc-based plated steel sheet comprising:
a steel sheet;
a zinc-based plating layer formed on the steel sheet; and
a post-treatment coating formed on the zinc-based plating layer, wherein 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,
wherein the post-treatment coating includes a metal oxide salt and an organic compound, the metal oxide salt including at least one metal selected from the group consisting of molybdenum (Mo), titanium (Ti), and zirconium (Zr), and
wherein an atomic ratio (O/M) of oxygen (O) to metal (M) derived from a metal oxide salt included in the post-treatment coating is greater than 2 and smaller than 20,
an atomic ratio (O/M) of oxygen and metal derived from a metal oxide salt of the coating upper portion is greater than 3.2, and
an atomic ratio (O/M) of oxygen and metal derived from a metal oxide salt of the coating lower portion is less than 5.
2. The zinc-based plated steel sheet of claim 1 , wherein
the atomic ratio (O/M) of oxygen and metal derived from the metal oxide salt of the coating upper portion is greater than 5, and
an atomic ratio (O/M) of oxygen and metal derived from the metal oxide salt of the coating lower portion is less than 3.2.