in complete contradiction to what neversaydie, said
use a gas blowlamp on the case around the threaded area, the ally will expand quicker than the stud, possibly spray the stud with penetrating oil briefly to cool it and hopefully get some in. If it cracks free and then jams dont force it but work it both ways, gradually the arc of movement will become more and more until it unscrews without fuss
Plenty of penetrating oil is the order of the day