I've made aluminum powder in a ball mill a few times, but my last batch began to smoke and caught on fire soon after I poured it from the tumbler. Nothing unusual was afoot. It was poured into a paper plate. The ball mill aggregate had steel bearings and a few rounded rocks, same as I had used before.
The only difference was I didn't place any charcoal along with the aluminum during the milling? So why would there be spontaneous combustion?