This is a very complex subject. Every metal has certain characteristics and the finished product needs to match the job. You can have a strong metal that takes certain stresses very well but will easily fail other types of stresses. Either way the metal can be strong but in different ways. I would think adding copper to aluminum would give it the ability to accept stresses where flexibility is needed. Aluminum though strong is brittle and doesn't take stress well and is so alloyed for the job. I realize some alloys give some substances totally different characteristics but is that the rule or more the exception. I don't know.

Maybe our resident expert here Mike Blue will chime in with an opinion.