Getting it expunged means that it doesn't show up on your civilian record for regular jobs, and your DMV record. However, nothing is actually completely gone. When the military looks into your record, it will show up, no matter how much time has gone by, no matter if it was expunged or not.
You need to tell them about it, because it will show up. If you tell them about it before it is better because you are honest. If you don't tell them, IT WILL SHOW UP, and they are going to look at you as being dishonest, and you will have no chance to get in.
I'm not sure if the air force will take you for what you did, but probably the army or national guard.