HARDCOAT. {Type III Coatings} Most Durable of Aluminum Finishes, Hardcoat can be produced in thickness ranges of .0002" to .0025"+ on most alloys.    The "File Hard" Aluminum Oxide formed by this process is Grey-to-Charcoal-to-Black depending on Base Alloy and Coating Thickness.  Hardcoat Offers:

• Superior Corrosion Resistance (336 ++ hrs salt spray) 
• Superior Wear and Anti-Galling Properties
• Electrical Insulation Properties
• User Designated Coating Thickness
• Unique "Half growth / Half penetration" simplifies engineering for close tolerance parts
• Subsequent option to Grind or Lap surfaces to exacting tolerances
• TEFLON treatments to improve lubricity

The "Controlling Document" for ANODIC COATINGS is Mil-A-8625.  All Customer Specs. follow the format and guidelines of those documents.  "Hardcoat" is designated as "Type III".  Seal options are "Class 1" (non-dyed) and "Class 2" (dyed).   .

The most commonly used alloys, Series 5000, 6000, and 7000 all produce excellent finishes.  Alloys with high concentrations of Copper, Silicone and/or Magnesium, however, have less desireable results and are not recommended.  The 2000 series, with its high copper content, is often prescribed because of its superior Strength characteristics even though there are challenges involved in processing. 

Additional Descriptions and Qualities available at the Aluminum Association Website at - http://www.anodizing.org/hcwebdoc.htm