Zn–Al-based metal–matrix composites with high stiffness and high viscoelastic damping

Abstract

A maximal product of stiffness and viscoelastic damping (E tan δ), a figure of merit for damping layers, is desirable for structural damping applications. Particulate-reinforced metal–matrix composites were prepared by ultrasonic agitation of the melt and composed of the zinc–aluminum (ZnAl) alloy Zn₈₀Al₂₀ (in wt%) as the lossy matrix and SiC or BaTiO₃ as the particulate reinforcements. ZnAl–SiC composites were stiffer and exhibited higher damping at acoustic frequencies in comparison to the base alloy. ZnAl–SiC composites were superior to Sn–SiC composites and possessed an E tan δ in excess of 0.6 GPa, the maximum figure of merit provided by commercial polymer damping layers. Furthermore, ZnAl–SiC composites displayed a high figure of merit over a broad temperature range. ZnAl–BaTiO₃ composites exhibited anomalies in modulus and damping associated with partial restraint of the phase transformation; one specimen was much stiffer than diamond over a narrow temperature range.