Phosphating is a treatment process that transforms the surface of steel into an iron phosphate layer. It is mainly used as a preparatory step before applying another corrosion protection method. The phosphate layer generally contains crystals of iron, zinc, or manganese.This technique is also referred to as phosphate treatment or phosphate conversion coating.This technique is also referred to as phosphate treatment or phosphate conversion coating.
Phosphate coatings are commonly utilized on materials such as carbon steel, low-alloy steel, and cast iron. The treatment involves immersing the metal into a bath containing a blend of iron phosphate compounds dissolved in phosphoric acid. When the metal surface interacts with this acidic solution, a chemical exchange takes place—this reaction diminishes the presence of hydronium ions (H₃O⁺), causes a rise in alkalinity (pH), and triggers the crystallization of salts from the solution onto the metal. Simultaneously, the interaction between the acid and the metal forms iron phosphate, which adheres to the surface as a uniform, protective film.
The following is a typical phosphating procedure:
- ✔️ Cleaning the surface
- ✔️ Rinsing
- ✔️ Surface activation
- ✔️ Phosphating
- ✔️ Rinsing
- ✔️ Drying
Phosphating helps in two primary objectives
- Corrosion protection in conjunction with powder coating
- Providing strong adhesion bonding for subsequent painting or other organic coating
