A comparison of the manufacture and mechanical performance of porous aluminium and aluminium syntactic foams made by vacuum-assisted casting

This paper compares key aspects of the manufacture and mechanical performance of porous Al, made by replication using salt beads, and structurally similar syntactic metal foams, made by replacing the salt with porous, expanded glass particles. Despite significant increases in stiffness, strength and energy absorbed, power law relationships between properties and relative density demonstrate that adding expanded glass particles is a less efficient route to increasing performance than increasing the metal fraction. That said, merit indices do indicate that 20% savings in mass are possible for stiff beams by substituting aluminium with syntactic metal foams. The manufacturing process for syntactic metal foams is shown to be simpler, driven by the lower thermal mass of the expanded glass particles and no requirement to dissolve a space holder from the structure. The balance of good performance and good manufacturability demonstrated herein, coupled with predicted low costs for raw material and manufacturing, highlights the scope for syntactic metal foams containing weak expanded glass particles to be researched and developed more widely.