Foam behavior of solid glass spheres – Zn22Al2Cu composites under compression stresses

Solid glass spheres – Zn22Al2Cu composites, having different densities and microstructures, were elaborated and studied under compression. Their elaboration process involves alloy melting, spheres submersion into the liquid alloy and finally air cooling. The achieved composites with densities 2.6884, 2.7936 and 3.1219 g/cm³ were studied in casting and thermally induced, fine-grain matrix microstructures. Test samples of the composites were compressed at a 10⁻³ s⁻¹ strain rate, and their microstructure characterized before and after compression by using optical and scanning electron microscopes. Although they exhibit different compression behavior depending on their density and microstructure, all of them show an elastic region at low strains, reach their maximum stress (σ_max) at hundreds of MPa before the stress fall or collapse up to a lowest yield point (LYP), followed by an important plastic deformation at nearly constant stress (σ_p): beyond this plateau, an extra deformation can be limitedly reached only by a significant stress increase. This behavior under compression stresses is similar to that reported for metal foams, being the composites with fine microstructure which nearest behave to metal foams under this pattern. Nevertheless, the relative values of the elastic modulus, and maximum and plateau stresses do not follow the Ashby equations by changing the relative density. Generally, the studied composites behave as foams under compression, except for their peculiar parameters values (σ_max, LYP, and σ_p)