Epoxy bonds to aluminum better than steel. It is a matter of fact. Alot of the mid 90's Trek bikes were aluminum lugs 7000 series aluminum tubes/carbon tubes.

The actual reason for glueing aluminum rather than welding is the heat affected zone. Aluminum alloys can get over 25% of the stiffness/strength from the heat treatment alone.In order to properly construct an aluminum frame it must be welded then heat treated. Obviously with gluing this is not a problem. Trek only did it with the better frames & tubing.

The bond area should be a minimum 50% of the diameter of the tube. 1 1/2" tube needs a 3/4" deep lug.