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

A maximal product of stiffness and viscoelastic damping (E tan delta), 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 delta 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.