I repaired my fan with this: Aluminum repair kits, repair aluminum by welding with a Propane Torch - Alumiweld
If you work carefully you can fill the voids and then remove excess material with a Dremel tool. The fan blades melt at about the same temperature as the alumaweld, so watch out. Better I think, looking back on it, would be to use JB Weld or some similar marine, super strong epoxy. Build up the area and then remove excess with a small grinder, then paint with silver spray paint.