Looking at several cores from failed motors some will have a filler-type material that is inside the stack of laminates. This material is almost always silvery, and it does melt relatively low, leading me to believe it is aluminum (and thus recoverable for casting parts purposes). However I haven't found anything to indicate what it is, other than not Magnesium for obvious fire-testing reasons.
In the found photo below, the metal in question is at the top and bottom of the core; runs through the core (thin lines), and can be extracted through application of heat. It is not extremely shiny nor is it extremely dense (like zinc might be), and I'm unfamiliar with the different grades of 'pot metal' if I could determine that with testing.