Originally Posted by RawAlex

Ummm, calculate the amount of energy (in joules) required to raise the metal to that temperature. That is the amount of energy "lost" in the process of making aluminum to be able to be used for this sort of thing. Combining the aluminum alloy with water would (pound for pound) likely generate much less energy than was put into the system.

The same issue exists for corn based products, as the energy required to convert the product from corn to ethanol requires more energy than is left in the ethanol. It is a net loss production, because in it's natural state, the corn has very little potential energy of it's own (unless maybe you burn it directly). Oil and natural gas are attractive fuels because mother nature has done the converting, provide a base product that has the energy already in it.