In mild to moderate impacts, crash energy is absorbed not by the cast (or stamped) frame, but by replaceable components external to the frame itself.

For minor impacts, that's the bumper, energy absorbing foam, and/or impact absorbing pistons that sit behind the bumper or crash bar.

For moderate impacts, it's deformable crush cans that bolt onto the vehicle's frame (whether cast, stamped, extruded or hydroformed)