Is Aluminum Electrical Cable an OK Substitute for Copper?

They were used in new homes but the aluminum would get hot at junctions and start.fires

Aluminium wire is not used in small sizes any more as building wire because it has the tendency to work loose and cause fires. It is used in services and feeders, but even then it needs to be treated properly. A lot of places will not use aluminium wire at all because it's tendency to loosen even in larger sizes and has to be re-tightened every so often. It also corrodes easily so it needs to have an antioxidant applied on terminations to prevent this from happening.