Here is the direct link to the 1991 catalog mentioned above.

http://www.retrobike.co.uk/gallery2/.../Raleigh91.pdf

It is a European catalog printed in what appears to be German. You'll find an entire section on the Raleigh USA Technium line-up to include your Supercourse. The 1991 Technium lineup appears to employ steel tubes (tube type varies by model) and cast aluminum lugs bonded together using the Technium "process".

Team: Reynolds 753, Dura-Ace
Competition: Reynolds 531, Ultegra 600
Pro: Cro-Mo, 105
Supercourse: Cro-Mo, Exage 500EX
Olympian: Cro-Mo, Exage 300EX