Apparently they aren't solid axles after all.
As well, Fords product line has no influence on Dana making that decision. There are TONS of companies utilizing aluminum in the automotive sector for different parts. Anyone who sees the benefits of utilizing aluminum where they can, will use it. It's not a matter of because Ford is doing it, they are, it's a matter of looking at other resources to innovate your product and make it better whilst keeping costs at a certain parameter.
If it wasn't so expensive, I'm sure they would use chromoly. But that's more of a specialty material usually used in race applications.