When two metals are mixed together they become?

Whatever the two metals happen to be. Some metals will chemically react with each other, though, and they will form a larger-moleculed substance. Most of the time (whenever the metals don't react), the alloy will retain the most outstanding properties of each of the metals. You should be able to deduct the rest of the information on your own (go to Wikipedia and investigate the individual metals you want to know about; it's not crap anymore).