Dick; They likely used anodization or electroplating to coat the bare steel with aluminum and the publicity people just cooked up the term,"Aluminized". It is likely that the sheet metal was plated before they punched panels out of it to stop it from rusting in storage. I have run into similar plated metal in my car on the clock housing and the radio cabinet, both of which would have been better painted. Of course I don't know whether it is aluminum or zinc or even cadmium, which was what some radio chasis' were plated with, or how you would tell the difference unless it's oxidized. Perhaps there is a chemist out there who could devise a simple test for us? What is interesting is that in the 73' Imperial profit book, that is on the main site, they mention that the door sills are galvanized which is usually a coating of zinc. They also mention dipping the body in a phosphorus solution for rustproofing and later dipping it in primer. Maybe if someone can find a 67'/68' profit book they could tell you what this plating was for? If it were me I would paint the underside of this shelf just for security, I am sure that the lack of paint was by error and not by design. I do know that I have seen a number of C-bodied cars around town and they always rust in the same same places so this aluminum plating didn't help that much. Best Regards Arran Foster 1954 Imperial Newport Needing A left Side Taillight Bezel and other trim parts.