Coin, button or replica?

Hi 

I found this digging up the garden. I can't find a similar one on the Internet which makes me think it is a button or replica. Any help with identification is greatly appreciated. 

It says IMPCAESMAVRSEV ALEXANDER AVG

This doesn’t look like a genuine Roman coin. Probably this is a modern imitation of a Severus Alexander coin, just featuring the obverse only.