Since epoxy doesn't stick well to metal, we attempted to acid etch the aluminum centering rings with vinegar before epoxying them to the motor tube. Theoretically, the vinegar would etch the metal, leaving it rough enough for epoxy to stick. We didn't get this to work well with diluted vinegar for an hour, but we would like to try 100% vinegar overnight.
Commercially available products such as Gardobond should be considered in the future when structural bonds to aluminum are necessary. Additionally, more appropriate adhesives (polyurethanes and epoxies) can be selected compared to the 2000 series resin the team typically uses.
Chickenbolts (a bolt added when you super-duper trust your composite-metallic joint) may also be worth adding.