Sounds like you broke it, not dulled it. Look at the tool, is it dull?
Did you weld AL to it? Did you make it work in a huge pile of
unremoved chips.

I go by feel. You can look at the chips. If they are fine little wispy
things you got too much RPM vs feed.

Use a larger end mill if you possibly can.

With the right cutting conditions, an end mill lasts forever in AL.

Karl