Not really.

Manesium + Water != explosive

several thousand degrees + water = water turning into steam almost instantly.

As steam has a lower density than liquid water, the volume it occupies is greater for the same mass. I suppose it could be considered an explosive reaction, but it isn't inherently explosive the way gun powder or explosives are.

Caution- tossing water into magnesium may scatter debris, including burning magnesium flakes. You can make a nifty fireball by tossing a few ounces of water into a pot of molton wax that has ignited. <img src="/images/graemlins/smile.gif" alt="" />