I'd never heard of 'aluminum foam', but according to Wired online magazine it's proving very useful in high-speed trains.
Engineers in Chemitz, Germany unveiled a prototype high-speed train cab made with the stuff earlier this year. The composite material is built like a sandwich: Between two pieces of aluminum, each just two millimeters thick, is a 25-millimeter-thick layer of the “foam,” actually a low-density, sponge-like composite of magnesium, silicon, and copper, and aluminum. And like a good sandwich, there’s no glue. The layers are held together by metallic bonding, the electrostatic attraction of negatively charged electrons and positively charged ions.
The result is a material that’s 20 percent lighter than traditional fiberglass, which is commonly used on high-speed train cabs. That’s a big advantage when the goal is to move faster and more efficiently. Even better, it doesn’t come at the cost of a weaker train. “The outer shell is so stiff that you need no ribs inside,” says Dr. Thomas Hipke, head of lightweight construction at the Fraunhofer Institute for Machine Tools and Forming Technology, which helped to design the prototype train cab. Peel tests of aluminum foam—in which force is applied to pull apart the layers of the material—destroy the foam interior instead of breaking the bonds between the layers, demonstrating the strength of the bonding.
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“Aluminum foam has a very high and comfortable impact resistance, especially for small impacts like stones, bottles or just birds,” says Ralf Uhlig of Voith Engineering Services, which was involved in the construction of the prototype cab.
There's more at the link.
I wonder whether the same stuff would be useful to make boats, or RV's, or even light aircraft? If it's as strong and as light as claimed, it might be a genuine advance in the state of the art. What's its fire resistance like? I know some aluminum alloys are flammable (as the US and Royal Navies found out to their cost during the 1970's), and magnesium (which burns like crazy) is listed as a component of aluminum foam, so it might be very dangerous in a fire.
Does anyone have more information about other uses for aluminum foam at present? If so, please tell us more in Comments. I find this sort of thing very interesting.