Well, this question has been festering for 46 years, so I'll ask: aluminum seems to the dumbest material to make keys ..... were they so much cheaper to the maker, or was there some other reason to use them?
I can well remember the day I went with Mom to trade her '55 Prez hardtop in on a new '62 Hawk........the GT was just so beautiful (so was the '55, but we were tired of having the rust repaired). HaHa.....gorgeous as the GT was, something seemed sort of chintzy: the carpet, the vinyl seats were stiff and the rear trunk overlay was a cheap imitation of the real "grill" on the back of Lincolns. And the '55 had "real" keys instead of those cheap aluminum jobs that we hated on Dad's Chryslers.
We'd often leave the car unlocked rather than risk having to unlock it with the key......'specially in winter when the locks were even stiffer. They'd get bent and eventually break. For the life of me, I don't know why we didn't just have good copies made at a key shop.
I thought for a while that maybe the aluminum keys were easier on the ignition......but over the years have had plenty of worn-out ignitions to replace, so that wasn't it. Almost as mystifying as second-gear start!