Low-density expanded perlite–aluminium syntactic foam

This paper addresses an innovative syntactic foam (SF) formed by counter-gravity infiltration of a packed bed of low-cost expanded perlite (EP) particles with molten A356 aluminium. The uniform distribution of EP particles in foams causes an even density throughout the height. Due to the low density (~0.18 g/cm3) of EP, the average density of these foams is only 1.05 g/cm3 which is considerably lower than most studied SFs. Owing to the high porosity of the filler material (~94%), the total porosity of the new foam reaches 61%. Microstructural observations reveal no sign of damage or unintended EP particle infiltration. EP shows a good wettability whilst essentially no reaction occurs at the EP–metal interface. Under compression, EP/A356 syntactic foam shows stress–strain curves consisting of elastic, plateau and densification regions. On account of its consistent plateau stress (average value 30.8 MPa), large densification strain (almost 60%), and high energy absorption efficiency (88%) EP/A356 syntactic foam is an effective energy absorber.