From what I have heard soldering aluminum is a tricky process which requires tight process control. The problem is that aluminum forms a tenacious oxide which is difficult to remove and prevent from re-forming. In my work, when soldering to aluminum is required I have the parts plated with copper then tin and the plated surface then takes regular lead-tin solder.

I would seek advice regarding aluminum solder from the local welding supply outfit. I agree with AEO that for non-structural use adhesive or mechanical fasteners might be the most satisfactory. JB Weld seems to work well on clean, properly prepared surfaces.