elastic region of material on a stress-stain graph is where it suffers no permanent deformation, yielding is where it starts to deform/lose shape. ultimate stress is where it fails. aluminum does have a certain life, where it only can take so many cycle loadings before it fails.
I'd call around. phone calls are few for the most part. being that it is heated evenly, I am not sure it needs a jig... however when doing concentrated heat, ie welding, it would be beneficial to have a jig.
just a thought, you might want to call some of the wheel manufactures. they all heat treat
its late and I'm getting punchy.
best regards
-Jason