ya sounds about right for d/c lol reading up on it when i was buying my tig found that the a/c perfered for aluminum as the alternation of the ground and tourch create a ripple effect in the pool bringing your contaminants to the surface giving you that mirror pool to work with and know whats happening the d/c does not.
and yes i know the reversing the polarities for the d/c mig aluminum welding but from the sound of it you were having issues with the tig that were fixed buy the constant cooler wire feeding your pool keeping the temps in check and being that your constantly adding filler that way your also moving fast enough to keep the base metal cool enough to weld yet not blow through.
yup i actually was gonna try welding with the mig in aluminum... hell i even have a 2lb spool of aluminum wire lol just never did and picked up the tig maybe ill try it out one day when im bored just cause i can
damn see turned your thread into a welding discusion and back to the topic....
z