The Effect of Foaming Agents on the Thermal Behavior of Aluminum Precursors

Various foaming agents can be used to achieve foaming of the precursors obtained by using the powder metallurgy method. However, the thermal behavior of pure aluminum precursors with different foaming agents has been studied very little in recent times. For the production of aluminum foams with closed cells, 1 wt.% of calcium carbonate (CaCO₃), titanium hydride (TiH₂), heat-treated TiH₂ and zirconium hydride (ZrH₂) were used. The foaming capability of the compacted precursors was investigated at temperatures 700, 720 and 750 °C. CaCO₃ and TiH₂ showed the best foamability at all considered temperatures, while ZrH₂ achieved relatively good foaming only at the highest temperature, 750 °C. Due to their low onset temperature of the decomposition compared to the melting point of the unalloyed aluminum, in hydride-based foaming agents the drainage occurred at the bottom part of the foam samples. Among the investigated foaming agents, precursors with heat-treated TiH₂ had the worst foaming properties, while CaCO₃ showed the best foamability without the occurrence of drainage.