Russians have added porosity to aluminum so that it can be lower density than water. Ships with porous aluminum foam would be unsinkable even with holes in the hull so long as the water that leaks in does not go beyond the buoyancy of the aluminum foam.
Aluminum foam is produced by adding foaming gas into liquid metal during re-melting of the aluminum material. The porous materials can be used for increase of structures stiffness and sound and heat insulating proprieties, said the SPbPU’s Media-center.
“High porosity level can be used to decrease the density of structural elements, e.g. sheets. The density can be decreased even lower than the density of water. Such structural elements will be unsinkable. And its usage in shipbuilding will ensure unsinkability even with the leak in the hull”, says Oleg Panchenko, deputy head of the Laboratory of Light Materials and Structures SPbPU, one of the inventors.
In many cases, the carrying capacity of thin materials (1 mm or less) is sufficient for a lot of structures. But material with such thickness sometimes has geometric limitations (the thickness is too small for manipulation) or it can’t be joined without deformation. Due to pores in the porous material, it is possible to increase the thickness, maintaining the weight and increase the stiffness of the structure.
A similar technology has been patented in Japan, but it has a specific feature that produced material will always be entirely porous. Researchers of SPbPU found the way to produce the homogeneous and heterogeneous distribution of pores in the material. Because it is made of solid material it can be either porous if necessary or with thickening or solid structure. Using this technology double-layer sandwiches may be produced, where only one side is porous, or areas on the material with increased density for mechanical (bolts/studs) or welded joints may be created.
Patent for invention: No. 2619422 “Method for the production of a porous metal body made of aluminum alloy”. Date of state registration: May 15, 2017.