You'll get the same spam you are getting now - adding an alias won't reduce the amount of spam. It's just another address to use.
You can have up to 10 aliases on an account (adding them one at a time over a few weeks or months) - and many people use the aliases as throwaway addresses - they use them to sign up on websites (instead of using their primary address) and when the spam gets bad, they delete the alias and make a new one. You just need to make sure you don't delete an alias you use for important websites (like banking) or for a recovery address on another account.