Zinc phosphating is also well know as 7 tank process.

A high-quality conversion coating is essential for the durability of painted metal goods. The process of applying an inorganic conversion coating(phosphate) to a metallic surface involves removing any surface contaminants, then chemically converting the clean surface into a non-conductive, inorganic conversion coating. Conversion coatings increase the overall surface area and promote adhesion of the subsequently applied paint. In addition, conversion coatings change the chemical nature of the surface(It Forms zinc phosphate or iron phosphate) which increases corrosion resistance. It is these two functions, increasing surface area and changing the surface chemistry, that serve as a base for preparing the substrate material for paint finishes.

The process of Phosphating basically relies on the basic pickling reaction that will occur on the metal substrate if the process solution will come in contact with metal. The biggest benefit that Phosphating can give is corrosion protection and strong adhesion. Just like Phosphate Coating, the process of Phosphating is being used for steel parts.