Wear-resistance

The metal surface coating with zinc or manganese phosphate, in dedicated phosphating plants for wear-resistance, is mainly used to increase the wear and corrosion resistance and of the treated by increasing its self-lubricating and anti-wear function.

Alone or in combination with rust-inhibiting oils, waxes or other organic coatings, zinc and manganese phosphates are a low-cost alternative to electroplating. Although heavy zinc phosphates are normally considered superior for this application, both types of phosphates extend the shelf life of aftermarket replacement parts in corrosive environments.

To reduce break-in wear on adjacent moving surfaces, nonmetallic, oil absorptive zinc and manganese phosphate coatings on bearing surfaces permit rapid break-in of moving parts without scuffing or welding by preventing metal to metal contact. Additionally, the oil held by the crystals improves the lubrication of the treated surface and imparts corrosion resistance. Manganese phosphate is generally preferred for this application because of its higher wear resistance.

Where torque-tension requirements are needed, zinc and manganese phosphated fasteners, sealed with a lubricating oil, guarantee repeatable torque-tension relationships in those applications where automated assembly equipment cannot be continually adjusted to compensate for varying of surface conditions. Yet, the treated parts are protected from oxidation during storage.

When bonding organic coatings like paints and polymer films to metals, to reduce the electrochemical activity of the ferrous surface and form strong physical and chemical bonds with the coatings, zinc and manganese phosphates are widely used as a bare under adhesives (in rubber to metal bonding), paints, and other organic coatings. The highly absorbent phosphate crystals allow paint to penetrate into tiny fissures and also increase the total surface area available for bonding. Acting as a dielectric film that insulates the active anode and cathode centers which exist over the surface of the base metal, phosphate coatings retard corrosion "creep", extending the life of the finished product. Light zinc phosphate coatings with small, uniform crystal sizes produce the best bond.