Greetings,
A soldered joint to aluminium won't last. For a good
electrical connection to aluminium get some jointing compound
suitable for ensuring an electrical contact between dissimilar
metals without corrosion. One has to use the same stuff for
aluminium to aluminium connections as well or the aluminium will
oxidise at the joint. Required for long (HF) yagi elements.
Put the jointing compound on the cleaned aluminium and on
the wire then fasten them together; by clamp, screw whatever.
Some would tape up the joint so the jointing compound doesn't
blow or wash away.
There's an article in Radcom July 2005, p75 Technical topics, on
working with aluminium.
I've assisted engineers/technicians constructing/repairing HF
yagi's on which every single aluminium to anything connection
that has to conduct has the compound put on. Note that copper
corrodes aluminium and that tightly clamping aluminum is
useless at stopping oxidation in the joint. Take the joint
apart later and everything will be wet ...
Good luck.

, ZL2TTS