Researchers at Peter the Great St. Petersburg Polytechnic University (SPbPU) have developed a new foam-core aluminum sheet material that could greatly increase the buoyancy of aluminum-hulled vessels.
"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," said Oleg Panchenko, the deputy head of SPbPU's Laboratory of Light Materials and Structures. This means that a vessel built of hollow-core aluminum would have more reserve buoyancy in the event of flooding.
In addition, sandwich construction means more strength and stiffness for the same weight (for flat material). This advantage comes with a caveat: materials scientists and veteran surveyors warn that saltwater contact can degrade the foil-thin walls of the bubbles in aluminum foam, leading to loss of structural strength over time. In a paper in the journal Materials & Design in 2015, a team led by researcher Xingchuan Xia found that this saltwater "corrosion process dramatically deteriorates the yield strength and energy absorption capacity" of the foam.
SPbPU's patented process includes a method to create the foam where needed within the interior of the metal, and the panel is formed as an integral sheet without further fabrication or bonding. Thanks to this advancement, the core of SPbPU's material is well-protected by an outer layer of metal, but any saltwater ingress could still pose an additional risk of corrosion relative to solid materials. Xia et al. found that this problem may be reduced by making the foam out of an alloy containing one to two percent manganese – a normal amount for marine grade aluminum.