Phosphating treatment is a process in which the metal surface undergoes a chemical reaction in a dilute solution containing phosphoric acid, phosphate and other chemicals, and transforms into a complete, insoluble phosphate film with a moderate anti-corrosion effect. The formation of this type of conversion film is an artificially induced and controlled corrosion process.

The phosphating is widely used, it mainly determined by the type and thickness of the phosphating film. Thick film phosphating is often used as separate protection (immersion oil, grease, wax, etc.), electrical insulation (such as silicon steel sheet), wear resistance, cold forming (pulling, drawing, cold extrusion, stamping, etc.), thin film phosphating is mainly used for inter-process protection and as a substrate for organic coatings such as paints and powders.

1. Classification of phosphating

(1) Classified according to the conversion form of phosphating film

1. Conversion phosphating: the solution corrodes the metal substrate, and the metal substrate provides cations combined with P043- in the solution to form a phosphating film (such as iron-based film).

2. Pseudo-conversion phosphating: Phosphating in which the main cations (zinc, manganese, chromium) in the film are provided by the solution.

(2) Classification according to the composition of phosphating solution and phosphating film

There are zinc-based, manganese-based, zinc-calcium-based, zinc-manganese-based, iron-based, calcium-based, zinc-manganese-nickel-based, zinc-manganese-nickel-calcium-based, etc.

(3) Classified according to the crystalline shape of the phosphating film

1. Crystal type: such as zinc phosphate film, zinc manganese phosphate film, zinc calcium phosphate film, iron (II) phosphate film, manganese iron phosphate film, etc.

2. Amorphous: mainly iron (Ⅲ) series phosphating film.

(4)Classified by film weight and use