This reminds me of burning scrap VW engine blocks or transmission cases. It can be done on an ordinary wood camp fire. You'll probably want to cut up the scrap into more manageable chunks rather than go for the whole thing at once. Then, toss a few into the hottest part of the fire. For about a half hour, nothing will happen. Then, the chunks will begin to melt, forming puddles onto the bed of coals, where they will ignite.

It is interesting that the pools of liquid metal burn quite slowly in the middle of the regular fire; you will only get a bright orange flame rather than the spectacle promised. Maybe only 5x as bright as a normal fire. But, if you scoop some up onto a stick (a long piece of steel angle iron is recommended) and pull it out of the fire into open air, it will burn with the brilliant white flame with which you are generally familiar.

For the finale, plunge the end of the stick into a large bucket of water, where you will observe the magnesium blob continue to burn while submerged for several seconds. Do not attempt to do this the opposite way by dumping the bucket onto the fire; an explosion will result instead. In fact, keep all moisture away from the fire in general. If you need to put the fire out for any reason, too bad.

After the fire burns itself out, the next day you might find some solidified blobs of unburnt magnesium. Be sure to remove all of these so you do not have an unexpected experience the next time you have a fire there. I have quite a nice piece where the magnesium flowed around a stick, but did not ignite.

This comment comes with the obvious disclaimer that nobody anywhere should try this for any reason, especially not the reason of fun.