What exactly are your concerns? In general, if you cold work a heat-treated aluminum alloy too much it will either resist your hammer blows and not form or crack. In my experience, I doubt you will ever get to that point fabricating your ribs in that manner nor is it something I usually worry about even when I flow-form parts with a rivet gun.
you build your form blocks with a relief angle cut into them.
T-18 as well.
Yes they did, twice. Unless you have a different definition of work hardened?
PE Mechanical engineer in Machine design here, with a materials emphasis. While this topic isn't quite as simple as putting a PT6 on a Piper Arrow it's also not rocket surgery.
Work hardening isn't a on/off switch - it isn't binary. It will gradually get harder as you work the material repeatedly, and eventually will be come brittle enough to fracture rather than deform. Aluminum can be annealed to undo work hardening.
And just to add, it can happen when bending in only one direction. For example, if forming a compound curve with a tight radius you'll probably have to anneal the piece half a dozen times to complete the bend and forming especially when using 1100 or 3003 aluminum.
Pounding on it for a long time work-hardens it. An aluminum rivet will work-harden if too many blows are required to set it. It needs to be formed with as few blows as practicable. That aluminum rib also needs to be formed with minimal working.
You can see, with the naked eye, microcracking along the outside of the bend. The surface becomes dull.
Neither of those statements are true, and also the grain structure won't necessarily indicate the work hardening. You can test hardness with Brinell or Mohs Hardness tester which comparing to an annealed sample will tell you how work hardened it's become.
You can measure hardness with a number of different (mostly destructive) methods but the only way to actually see if you are starting to work harden a part is by looking at the grain boundaries. All the other methods will only tell you after it has already become hardened a significant amount.
And you will also destroy the original temper... because, you know, annealing will do that
