Tapcons would certainly work as would any kind of sleeve/screw combination (with the latter I'd use stainless steel screws). Might not hurt to put down a nice, thick bead of silicone behind the threshold to keep out any water.

It is not going to last all that long unless you take steps to keep the aluminum from direct contact with the concrete.

A strip of EPDM barely wider then the aluminum is all it takes.