Ok, I’m assuming you know that the Ali should be annealed before bending?
There’s a trick that you can use to know how much heat to apply. Rub some soap (old fashioned stuff, comes in blocks, used for washing hands etc) on one face of the Ali along the line you want to fold. Gently heat the other side of the fold line with a flame (blow torch is fine). Watch the soap stains and they will turn brown, when they do the Ali is annealed. Best to play the flame along the full fold length rather than do one bit at a time.
The Ali will both age and work harden so once annealed fold it within an hour or so - doesn’t need to be folded hot or warm
Failure to anneal will introduce potentially catastrophic stresses into the sheet Ali.
It depends what aluminium it is...
1050 H14 which is what most people will sell you is perfectly fine to bend without annealing- in fact its not heat treatable so it wouldnt do anything
3003 and 5251 (old NS4) are tougher, but still bend with out annealing
6061 and 6082 absolutely need annealing before bending
