It’s a chemical process that alters the surface of the metal parts through the creation of phosphate crystals, chemically bonded to the substrate. The efficacy of this technique rely on the properties of these compounds that are able to improve the material resistance to the corrosion and facilitate the adhesion of the following painting processes.
However, this treatment gives a lower level of protection than zinc coatings in mild environments. An effective protection against rust can be only obtained by a further layer of oil applied on the surface and retained by the porosity of the coating.
The phosphate coatings are a commonly used for the treatments of iron and iron alloys and largely used in the automotive industry because of able to fulfil the high standard requested by this sector in terms of corrosion resistance. The treatment can be applied by means of spray systems or immersion. The immersion system provides better results because is more efficient in reaching difficult areas of the parts and moreover has different characteristics. In addition to this the process uses zinc or manganese to trigger the chemical reaction. However, manganese phosphate coatings provide a more durable wear resistance of the material in comparison to zinc phosphate coatings.
In addition, phosphatizing with manganese is used mainly in mechanical as reduces, but above all makes homogeneous, the coefficient of friction ensuring greater accuracy in the preload of the joint.
The phosphate coating provides a good base for further coatings or treatments too. The thickness of the coating varies between 4 and 12 µm.