Directional Solidification and Microsegregation in a Magnesium-Aluminum-Calcium Alloy.

Creep-resistant Mg-4Al-4Ca (AX44) alloy was solidified under different growth/cooling rates using a directional solidification (DS) technique. The solidification behavior and microsegregation of the alloying elements in the castings was investigated. Computational thermodynamics calculations of phase equilibria and experimental observations confirm that the solidification microstructure in this alloy consists of α-Mg, C36-(Mg,Al)Ca, and C14-MgCa phases. A relationship was established between the primary dendrite arm spacing and the cooling rate, which can be used to predict mechanical properties such as yield strength and creep. The microsegregation of alloying elements (Al and Ca) predicted by the Scheil model in AX44 agrees well with the electron probe microanalysis (EPMA) measurements, suggesting that the Scheil model can be used in microstructure simulation of magnesium castings. [ABSTRACT FROM AUTHOR]