On the fabricability of a composite material containing the FCC matrix with embedded ductile B2 intermetallics

An imaginary composite material containing a ductile Al-rich FCC matrix with embedded particles of ductile RMg intermetallics (R is a rare-earth metal) may possess high strength and formability thus making it suitable as a replacement for steel in automotive applications. Although different fabrications routes can be explored, a direct-chill casting is likely least expensive of them. A crucial question is whether it is possible to find such a composition of the ternary Al-R-Mg melt whose solidification would result in the desired Al/RMg structure. In order to answer the question, a thermodynamic model of the Al-La-Mg system was built using the CALPHAD method. The model, whose validity was demonstrated by calorimetric experiments, was then used to prove that the FCC + LaMg composite material could not be produced via casting. Similar properties of rare-earth metals suggest that the conclusion based on the analysis of the particular Al-La-Mg case, will likely remain valid for other rare-earth elements.