Ha, here is my magnesium and welder story.
I worked in a shop where we made insulation blowing machines. We made a nozzle for fire proofing, sprayed glue with cellulose to coat beams in high rise buldings. the nozzles were sold as "lightest weight" and were made of cast and machined Magnesum. One of the shop guys knew the stuff was special and saved all the lathe scraps in a 5 gallon paint bucket.
So then one day a different guy was using the cutting torch without noticing the bucket laying there and ignited the magnesum with started burning "White hot". Looked like flash bulbs all going off at once.
So the supervisor (and also a son at Meyer & Sons where i worked hussled the bucket outside and without thinking turned the hose on it.
so here is formula:
Take on burning bucket of Magnesuim @ ~ 3000 degrees
Add water > Which both vaporizes and breaks down on contact (this is why you use foam on hot fires)
Release hydrogin and O2 into ~3000 degree bucket = Fire ball was about 10 feet in diameter and went up a bout 25 feet removing all the hair from the bosses son.
PS: don't try this at home (do it at work!