There are lots of different aluminum alloys, with different properties. In FRC the most common is called 6061.

Use aluminum for things that don't need to be flexible, like gussets and brackets.

We use 1/8" and 1/4" thick aluminum, use 1/4" for things that need a lot of strength, and 1/8" for things that can get away with being weaker in that direction, like gussets under shear loads.

Polycarbonate is used for things that benefit from being flexible, like intakes.

We use both polycarb sheets for mechanism plates, and polycarb tubes for intakes.

DO NOT USE LOCTITE ON POLYCARB. Using LocTite on polycarb causes cracking and structural damage.