Anodize Pits on 2024 Aluminum

snipped-for-privacy@molytunsten.com wrote in news:1189288639.888711.209570 @w3g2000hsg.googlegroups.com:

Some possible causes: Impurities in the material Too high of a current. Insufficient flow. Bad distribution of alloying materials in the aluminum. Unclean surfaces would normally result in non-anodized areas, but depending on the contamination material, it's possibly a cause.

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

I was told you can only use alum. racks for 2000 series alum.