Learjet has expressed the feeling of "the trade" ... if not that of the wire manufacturers!
Aluminum, anywhere near the ground, can't help but have corrosion issues. Nor have I ever seen a landscape lighting transformer listed for use with aluminum wire. As far as I know, aluminum is not currently made in wire finer than #6. (I could be wrong on that).
Indeed, the only place I see aluminum used is in the PoCo service drops.
But, before I get my shorts in a know over "can I or can't I," I'd look to see if the stuff exists first of all.
