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

A maximal product of stiffness and viscoelastic damping (E tan d), 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 d in excess of 0.6GPa, 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.