Foaming behavior of powder metallurgical Al–Sn foams

Foaming Al by the powder metallurgy technique was investigated with Sn additions (⩽5 wt.%). The low melting point of Sn and its immiscibility with Al creates integrity of the powder mixture during hot compaction and foaming. Furthermore, it decreases the surface tension of Al, reducing pore coalescence. Different alloying compositions and pressing and foaming parameters were evaluated. The materials were characterized using differential scanning calorimetry and thermodynamic simulation. Foam expansion and pore shape were studied by the construction of expansion maps and image analysis on foam cross-sections. It was established that, with Sn additions, not only is foaming possible at lower temperatures, but also the Sn stabilizes the foam, preventing collapse. The number of pores and sphericity values increased with increasing Sn concentrations. Optimized process parameters leading to an expansion of 375% for up to 10 min were achieved with 2–3 wt.% Sn additions, hot pressing at 300 °C followed by foaming at 725 °C.