What is a strong glue for bonding metal?
This-to-That recommends JB-weld or LePage's Metal Epoxy.  I've never used either, personally.

The important thing for this is going to be surface prep and clamping, I would assume.

You might be able to use a CA glue (ie, "super glue"), but you'll need additional reinforcement to keep the bond from shearing (eg, glue then bolt it in place, but 1/4" is kinda narrow to bolt through; also, I have no idea what sort of clearance issues there might be if there are bolts sticking out)