Zn-matrix syntactic foams: Effect of heat treatment on microstructure and compressive properties

Glass microballoon filled ZA8 alloy matrix syntactic foams are studied for the effect of heat treatment on the microstructure, compressive properties and energy absorption capacity. Normalizing and quenching resulted in reduction or dissolution of eutectic (α + η) phase in the matrix alloy. Blocky Al3Ni precipitates were observed in the matrix due to the reaction between matrix and the nickel coating of the particles. The average density and porosity of the syntactic foam were around 3 g/cm3 and 51.5%, respectively. The heat-treated composites had higher yield strength, compressive strength, plateau stress, densification strain and energy absorption capacity than the as-cast composite. The normalized and quenched composites showed the highest compressive strength, plateau stress and energy absorption capacity. In fact, their highest values were 216.8 MPa and 211.9 MPa, 226.9 MPa and 223.4 MPa, and 125.3 MJ/m3 and 117.7 MJ/m3, respectively. The improvement in the compressive properties is attributed to composition homogenization of alloying elements and relief of the residual stresses. The superior properties of syntactic foams compared to those of the conventional metal foams suggest their potential applications in marine vessels and submarine structures.