I'm guessing the hole will be something like 35mm to 50mm in diameter? Here's how I used to do it with simplest equipment.
Take a compus and draw a circle in the exact diameter I need.
Draw another circle (concentric) that is smaller. The size of this hole will depend on the drill bit you use.
Drill a bunch of holes all around the circumference of this smaller hole. I used to use 3mm bits.
Make sure, the outer edge of the holes are about 0.5 to 1mm inside of the outer (original) circle.
Then use a diagonal clipper or a small saw and connect the holes, so the disk can be removed.
Use a half round file to smooth it out to the diameter of the outer (original) circle.
It's not that much of work, if you are talking about relatively thin aluminum material.