What I have done that seems to really help is to get a greenpad dipped in
cleaning solution and scratch off the oxide surface. I then quickly dip it
in a bucket of water to rinse it off and then dip it immediately in to the
Alodine solution.

>Aluminum oxidizes *amazingly* fast.  Knowledgable people have told me that
I've never actually seen bare aluminum -- it oxidizes as fast as it can be
exposed to air, even on a lathe or milling machine.  So that's the reason
for keeping the aluminum wet before brushing, dipping, swabbing on the
alodine.
Keeps the oxygen away.