I believe Alumina can be joined to Aluminum. However, I do not have a certain answer. I was trying to read about Aluminum and Alumina joining. I came across one picture over some article referenced as "Diffusion bonding of stainless steels to alumina using aluminum interlayers" Journal of Materials Science, 17, 1982, p. 3347.

Picture describes a bond with alumina as base metal and aluminum as interlayer.
Venu Krishnardula
Auburn University