Stable (non flammable) above a certain thickness I believe. Bike frames made of magnesium were available in the 90's if I recall correctly.
Presumably has better mechanical properties than Aluminium (which also goes kaboom in powdered form).
"Magnesium alloys are mixtures of magnesium with other metals, often aluminum, zinc, manganese, silicon, copper, rare earths and zirconium. "
They maintain much of the light weight nature of the magnesium but loose the nasty habit of oxidizing when it gets hot, magnox reactors had a magnesium-aluminum alloy in the components of the reactor hence the name (magnesium non-oxidizing).