Benefits of Zinc and Manganese
Phosphate Conversion Coatings
Both coatings are applied for the following benefits:

• Paint and Coating Primer
• Increased Oil and Lubricant Adhesion
• Anti-Galling Properties
• Corrosion and Rust Inhibition: Phosphatized parts can withstand up to 240 hours of salt spray without signs of corrosion.
• Thin Coating/No Distortion: Screws and threaded parts can be phosphatized.
• Cost Efficient: It's cheaper to phosphatize hidden parts, springs, bearings etc. than to paint or plate them.
• Aesthetic Appeal: The blue-gray coating is often more appealing than the unfinished metal.

Zinc phosphate is particularly useful during certain processes such as wire-drawing. The nature of the zinc phosphate coating allows the adhesion of lubricants even under extreme heat and pressure. Zinc phosphate is used often in the auto and appliance industries.

Manganese phosphate is the thicker of the two phosphate coatings. Its crystal structure retains more lubrication than zinc phosphate and is favored for its superior anti-galling properties.

How Phosphatizing Works
To apply the phosphate coating, parts can be either bathed in the phosphatizing chemicals or the chemicals can be sprayed onto the metal using a system similar to a conventional pressure-washer. In either case the solution applied to the metal is composed of four parts: detergents, metal phosphates (in our case zinc- or manganese-phosphate), phosphoric acid, and additional agents (such as reaction catalysts or chemicals to tie-up bi-products). The detergents help to clean and degrease the surface of the metal. The phosphoric acid provides for minor acid etching or picking allowing for better paint and lubrication adhesion. The metal phosphates react with the surface of the part to form the corrosion-resistant phosphate coating.

The reactions involved are as follows:

First, the iron comes into contact with the phosphoric acid causing acid pickling. Iron (Fe) is oxidized and hydrogen ions (H+) ions are separated from the phosphoric acid and reduced to form hydrogen gas (H2). Some of the oxidized iron sloughs off or dissolves leaving the surface acid-etched.

In the second reaction, the zinc phosphates are deposited onto the substrate to form the conversion coating.

For more about phosphatizing, select one of the following:

Overview  |  Technical Information  |  Photographs

For more information about Phosphatizing, or other treatments offered by Superior Shot Peening, click on one of the following:

• Shot Peening
  
  
• Esonix UIT
  
  
• Phosphatizing
  
  
  • Overview
    
    
  • Technical Information
    
    
  • Photographs
    
    
• Salt Bath Heat Treating
  
  
• Passivation
  
  
• Abrasive Blasting and Deburring
  
  
• Special Refurbishing Processes