What exactly are the rules when forging metals togather as liquids, and then to cool down into a soild? Will the less dense metal raise to the top. Could it be possible to mix metals like titanium and aluminum.

It's complicated, some metals mix- like tin and lead.

Some don't- like zinc and lead.

 

The Aluminium + Titanium phase diagram is rather complicated.

http://www.calphad.com/titanium-aluminum.html