Magnesium alloy started to come into use later, with the latest pro-level cameras being made differently as well- a cast body which constitutes the exterior as well as the chassis.
The LX has a die-cast aluminum body and cover plates, which are anodized and clear-coated. Titanium cameras, like the OM-4T, LX Titanium, Nikon F3T, etc, have titanium covers, not titanium chassis.
Brass was used widely as a cover material because it was soft enough to be easily drawn into the shapes needed, yet would deform rather than crack from impact. Being easy to shape with few problems, it was well suited to mass production.