I use 2024 T351 aluminum for my molds, because it is warpage free, and takes a pounding as well as any other.
Pounding is the right word, and beating is good one too. Better than any of the four letter words that also fit mould abuse.. Most casters don't beat them, and knocking sprues with a piece of wood won't hurt the molds if some thought goes into the blows.
If one can hear the mold go closed it is wise to slow the closing down a little till the sound is just a soft click. If it cracks shut, it is getting pounded, and any metal will show the grief after some use. So though cast iron or steel will stand more pounding than aluminum, it will still suffer, so why not use nice light warp free, and more corrosion resistant aluminum?