Phosphate coatings are produced on ferrous and nonferrous metal surfaces and are composed of tiny crystlas of iron, zinc, or manganese phosphates. These inorganic coatings produced on meatl surfaces retard corrosion and promote better paint bonding. Phosphate coatings are produced after precleaning or are formed in a combination bath known as cleaner-phosphate. Phosphate coating are generally used by the metal finishing industry for the following reasons:
• To provide a base for bonding organic finishes such as paints, lacquers, plastics, rubber, adhesives, etc.
• To provide a base of oils, waxes, and rust preventives to reduce metal corrosion.
• To provide a base for lubricant on bearing surfaces to reduce friction.
• To aid in drawing and forming of metals.