There are two standard specifications for anodic oxide coatings on Al: MIL-A-8625F and ASTM B 580 - 79 (1995). MIL-A-8625F is available for free from the following website:
ASTM B 580 can be purchased through a number of entities:
ASTM at
ASM International at
Global Engineering Documents at
The types or classes fall into two general categories: hardcoat anodizing and not hardcoat anodizing. Typical anodizing baths use either chromic acid or sulfuric acid as a source of oxygen. The coating thickness from these baths is usually ~ 1-10 micrometers in thickness. These coatings can be subsequently sealed, or painted over, etc.
Hardcoat anodizing is typically performed in sulfuric acid baths, resulting in much thicker coatings: ~ 50 micrometers. This produces much better resistance to wear and abrasion. Upong sealing, these coatings also provide outstanding corrosion resistance.
There has been at least one other thread on eng-tips regarding anodizing, so use the SEARCH function and find it, as I posted some information there as well. An excellent website with technical information on the various anodizing processes is
which is the website for Metalast Inc., a commercial coating company in the U.S. that specializes in anodizing. Another good source of information is Volume 5 of the ASM Handbook, titled
Surface Engineering. The section on Anodizing is about 11 pages. A good university library should have this book, or you can visit the ASM website that I included earlier for more info.
