The Home Machinist!

A technique I use to anneal aluminum is to deposit a light to medium coat of soot from a acetylene only torch flame to one side of the sheet metal, then add oxegen to the flame and burn off the carbon. You need to keep the torch moving quickly to avoid overheating any one spot which could ruin the metal. Air cool and it will be soft. Forming or shaping the metal by stretching and shrinking work hardens the metal and the process can be repeated if necessary.
This can also be applied to aluminum tubing which I find a lot in 6061, prior to bending in a tube bender where 3-6" center line radius bends will crack the tubing.

warmstrong1955 wrote:I would think that aluminum sheet, no doubt depending on the alloy, could be annealed with some patience, and a propane torch, and left to air cool....which wouldn't take long. l

Air cooling is not required, as aluminum does not harden by the carbon cycle. Once heated to an appropriate temperature, it can be cooled quickly if desired. Quenching is very much a part of the solution annealing process, from which aluminum can then be properly heat treated. Same thing applies to copper alloys. Quenching isn't required, but offers benefits, such as cleaning the surface.

Harold