cliff notes:
a 28 gram flashlight made of solid aluminium, would weight 18 grams if made of magnesium alloy, a savings about 1/3 the weight of the body.

magnesium alloy oxidizes, because it contains aluminium

magnesium burns:
it is used in firestarters

I can see it now… LiIon vents with fire, the magnesium flashlight body joins the thermal runaway

and we get a campfire:
“Water pisses it off!”