Just to chime in on this, magnesium has made great strides since the days of the Kirk cast bike. I've had involvement with the material as it relates to bike, auto and motorcycle applications, and actually have a modern bike with welded tubing made by the folks who originally supplied Paketa. It's a 2lb (54cm) frame with ride characteristics most like a good ole Reynolds 531 (classic content?) frame. It's major advantage aside from its weight is vibration dampening, which gives it a very smooth feel on the road. Corrosion is less of an issue than in the past, there is no fire danger in the current alloys used in bikes, in fact, the company that developed the welding process is in, ahem, the aerospace industry. It built missiles and fighter jets for the Russian government until the fall of the Soviet Union. Other processes are being perfected, one being by a South African company, that has become a supplier of bike frames as well. Merida, the Taiwanese giant and half owner of Specialized has Mg frames on the market everywhere but the US, but has not perfected the process as yet to pass fatigue testing. For now, it's the new wonder metal. I've been riding mine for four years and still love it.
thinking about cryogenically treated metals harvested from salt water,