Originally Posted by
popeye
You want to use a malleable AL alloy as it needs the ability to be repeatedly bent not broken
Malleability is not the design purpose of an aluminum derailleur hanger, since aluminum won't tolerate much bending without breaking.
The derailleur hanger is designed to be substantially weaker than the dropout and frame. A broken hanger is far preferable to a bent or broken frame.
Some
6061 aluminum sheet ought to suit just fine. It's fairly strong (as aluminum goes), very commonly available, and not terribly expensive.
A slightly bent hanger can be straightened. If the bend is substantial, it's time to replace it.