Solidification of Al-4.5 wt pct Cu-Replicated Foams

Microcellular Al-4.5 wt pct Cu of 400- or 75-mu m average pore diameter is solidified at cooling rates ranging from -30 K/min to -0.45 K/min (-30 A degrees C/min to -0.45 A degrees C/min). In the 400-mu m pore size samples, the dendritic character is lost, and the level of microsegregation, which is quantified by the minimum copper content of the matrix, is reduced when the cooling rate is lowered. The 75-mu m pore size samples show no dendritic microstructural features and low levels of microsegregation, even at the higher cooling rates explored. Microstructural maps, based on solidification theory developed for metal matrix composites, satisfactorily describe the microstructure of the Al-4.5 wt pct Cu foams. A finite difference model giving the minimum copper content as a function of the reinforcement size and cooling rate, developed for fiber-reinforced metals, is also valid for replicated Al-4.5 wt pct Cu foam. This work thus extends to particulate composites and, by extension, to replicated microcellular alloys, results originally derived from the study of fiber-reinforced metal solidification.