A phosphate coating is the treatment of iron or steel by immersing it in a solution of phosphoric
acid and phosphate salts creating a layer of crystalline phosphates on the surface of the part.
There are three types of phosphate coatings; zinc, manganese, and iron. Depending on which
of these types is used and the surface condition of the part the resulting finish will consist of
translucent crystals that are light gray to black in color.
Phosphate coatings often have oil or another type of sealer applied to provide maximum
corrosion protection. The porous nature of the phosphate finish allows the oil or sealers to seep
into the phosphate coating and become interlocked after drying.
Manganese and zinc phosphates are used by the automotive, defense, firearms and machinery
industries for corrosion protection and lubricity. Zinc and iron phosphate can also be used as a
paint / coating base.
Typical specifications for phosphate include DOD-P-16232 and Mil-DTL-16232
