Aluminum needs to be handled with kid gloves or will scratch up. This is because the material wants to drag over the top of the female die as the bend is being made.
Might I suggest UHMW for your die block? It is a breeze to machine, and is tough enough for something like what you are doing. Just make it a bit overwidth, so that you can radius the top corners of the female half, as they do the brunt of the work and will deform after repeated use if left sharp and pointy.
Or, you could make a metal die set out of cheap steel, and overlay the surface with some 1/8" UHMW pads to protect your part. Suitable allowance for the altered radius can be built in to your machining plan.
There will be some springback of the material. I do not know how to predict that, other than to take a wild guess after an experiment or two with a crude die involving welding a couple of round parallel bars to a backplate and pressing a sample part in between to a depth stop.
The pressure required to make the material take a new set is fairly high. While a 12 ton would do the rough bend, the material nearest the edges of the part, closest to the supporting edges of the female die, takes lots of pressure to get that last little bit of roundness to 'take'. This high pressure requirement can be reduced if you do the center bend, then rotate the part to reapply the pressure near the edges, with the edge more centered in the die. I think it could be done with a 20 ton hand press, if you just have a few to do. You can never have a press too big when bending stuff
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)