Partitioning of Solute to the Primary α-Mg Phase in Creep-Resistant Mg-Al-Ca–Based Cast Alloys

Abstract

The partitioning of elements during solidification of ternary and quaternary Mg-Al-Ca alloys has been measured by an electron microprobe segregation mapping technique. Differences in the degree of partitioning of Al and Ca to the α-Mg phase in as-solidified MRI230D, AX44, AXJ530, and MRI153M alloys was observed. MRI230D has a higher level of Al and Ca in the primary α-Mg phase, while only a higher level of Al is observed in MRI153M, compared with AX44 and AXJ530. While the increased levels of Al in the MRI alloys may be due in part to higher bulk Al concentrations, the higher level of Ca in the primary phase of MRI230D is attributable to the presence of Sn in this alloy. The differences in the partitioning of Al and Ca to the primary α-Mg phase during solidification influence both solid solution and precipitation strengthening, which can explain observed differences in creep behavior.