DIYbanter - Anodize Pits on 2024 Aluminum

On Sep 8, 2:57 pm, wrote:
Somehow when we anodize 2024 aluminum using titanium racks, we almost
always experience some pitting problem. Why?

Thank you.
Where do you see the pits? Can you inspect the parts for pits after
andozing? If the pitting is occurring in the anodize tank, then
chloride ion contamination is probably responsible.

The theory is that the pitting was most likely caused by galnavic
effect between aluminum parts and titanium rack in the chromic acid
solution with a certain amount of chloride ion. For some reasons, your
chromic acid has been contaimnated with cholrides. Typically the
chloride level should be 0.010 gm/l max. If chloride is the problem,
you may need to change your source of chromic acid, and get a chemical
analysis from any potential source.

Of course the pitting could be occurring in the seal bath. (Again,
check parts before and after seal for pits). If the pitting is
occuring during seal process, you can eliminate the pitting of black
dyed sulfuric anodized 2024 parts on titanium racks by hanging
magnesium rods next to the racks. Magnesium is even more anodic than
aluminum, and robs the galvanic currents away from the parts.

Ken

Torrey Hills Technologies, LLC
www.threerollmill.com
www.torreyhillstech.com