Carbonates as foaming agent in chip-based aluminium foam precursor

Replacement of TiH2 as foaming agent by CaCO3 (lime) and CaMg(CO3)2 (dolomite) for AlMg4.5- and AlSi9Cu3-foams was investigated considering influences on foaming capability and cellular structure. Precursor materials were produced from alloy chip and powder mixtures by means of the thixocasting process. AlSi9Cu3 variants showed expansion levels sufficient for commercial use. Variations in expansion observed when CaCO3 and CaMg(CO3)2 were compared as foaming agent are explained based on the course of decomposition. Improved performance of dolomite-based foams relies on formation of stabilizing MgO phases, which do not develop during decomposition of CaCO3 in Al-Si-Cu alloys.