Just one of those funny tuts

i need dem scientists and engineers to talk about this. . . . .
beeen wondering, wen a plane crashes, nothing happens to the black box
meanng its definately made of something different. .

somy question is

cant the same stuff be used to build the whole plane

The Black Box which is actually orange is made out of Heavy Reinforced Metals, or titanium. It can vary by manufacturer.
apart from the fact that building an entire aircraft out of these materials will make it ridiculously expensive, it will also make the aircraft too heavy to fly efficiently.

Even if you had an undamaged aircraft at the time of major impact, you'd still have damaged people inside.