Isn't anodizing the coloration process of aluminum's normal oxidation
process, of which alodyning is but one normally used on aircraft parts?
jofarr, soddy tn

Alodine is a chemical conversion coating done in a chromium bath that leaves
a conductive aluminum/chromium phosphate coating on the aluminum. Alodine is
an excellent preparation for painting, also. A yellow dye is often added so
a person can tell it was actually done, otherwise clear alodizing does not
look too different than normal aluminum, I think.

Anodizing is done for wear and corrosion resistance.  Anodizing is done in
an an acid bath, under DC electric current.  It causes a nonconductive
aluminum oxide layer on the part. It actually oxidizes the surface and forms
a thicker, (in some instances MUCH thicker) oxide layer than would form on
it's own in air. The coating as it comes out of the acid, is porous and can
be dyed various colors depending on the acid used (sulfuric acid results in
a grey to olive drab color and is usually only dyable dark colors like red,
blue, brown or black) prior to its sealing, usually with dichromate. The
process causes some growth to the part, the thickest and most wear resistant
being referd to as "Hard Anodizing".

Alodine is used where electrical conductivity (for grounding as an example),
or thermal conductivity (for heat sinks for instance) are important.
Anodizing is used where conductivity is not important but corrosion or wear
resistance is.

Information gleaned from a couple websites, and trimmed for us laymen.

Jim Beckman



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