The Influence of Foaming Agents on Aluminium Foam Cell Morphology

Abstract

The choice of foaming agent and its mass fraction significantly affect the size and number of metal foam cells. The powder metallurgy process was used to produce aluminium foams with the addition of various foaming agents: titanium hydride (TiH2) and calcium carbonate (CaCO3). TiH2 was added in an amount of 0.4 wt.%, while the quantity of CaCO3 varied between 3 and 5 wt.%. The produced foams, with approximately the same degree of porosity, were scanned using a non-destructive computed tomography method. The number, size, equivalent diameter, sphericity, and compactness of cells were analysed on the obtained three-dimensional models. The results showed that foams foamed with TiH2 have much larger cells compared to CaCO3 agent. By considering the influence of CaCO3 fraction on the morphology of aluminium foam, it follows that a smaller quantity of CaCO3 (3 wt.%) provides a macrostructure with smaller cells. Samples with five wt.% CaCO3 contain slightly larger cells but are still much smaller than foams with TiH2 foaming agent at the same degree of porosity. The sphericity and compactness indicate that TiH2 foaming agent forms cells of a more regular shape compared to CaCO3 agent.

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

“…Due to the significantly lower price, foaming with calcium carbonate (CaCO 3 ) has recently been increasingly investigated [29][30][31][32]. In addition to the financial benefits, the decomposition temperature, which starts at around 660 • C [29,33,34], is also an advantage for unalloyed aluminum that melts at 660 • C. In contrast to TiH 2 , which forms relatively large cells, CaCO 3 forms a finer morphological structure [35]. This is because foaming starts at the later stage when the temperature is close to the aluminum melting point.…”