Precipitation of the Al 2 Ca phase in the a-Mg phase of the Mg-Al-Ca-based AXJ530 die-cast alloy and the effect of precipitation hardening on the creep resistance were studied. Precipitation of the Al 2 Ca phase is suppressed in the die-casting process due to its high cooling rate, but precipitation was observed during subsequent isothermal heat treatments above 448 K. The precipitate has a disk-shaped morphology parallel to the basal plane of the a-Mg matrix phase and increases hardness by aging in the temperature range of 448 to 573 K. The creep resistance of the die-cast material at 448 K was improved by a factor of 1.5~2, by a peak-age heat treatment at 523 K for 1 hour. Improvement in strength is limited by the low volume fraction of the precipitates; however, the precipitates are effective obstacles against dislocations gliding on nonbasal planes during creep deformation.
The isothermal sections of the Mg-Al-Ca ternary system at 773 and 673 K were determined by phase analysis with electron-probe microanalysis (EPMA) and transmission electron microscopy (TEM). The C36 phase exists between the C14 (Mg 2 Ca) and C15 (Al 2 Ca) phases, and its stoichiometry is close to Mg 2 Al 4 Ca 3 . The ␣-Mg phase equilibrates with the C14 and C36 phases at 773 K, but with C14, C15, and  phases at 673 K, due to the decomposition of the C36 phase into C14 and C15 phases. These intermetallic phases have significant solid-solubility in the ternary system.
The effect of Sr additions on the microstructure and strength of a Mg-5Al-3Ca alloy was investigated by replacing Ca with Sr. In the as-cast alloys, the major intermetallic compound observed at the a-Mg dendrite cell boundary region changes from the Al-rich (Mg, Al) 2 Ca phase to the Mg-rich Mg 17 Sr 2 phase with increasing Sr content. This results in an increased Al solute content in the a-Mg phase in the high-Sr containing alloys. More than 1 wt pct of Sr enhances the solid-solution strength of the a-Mg phase, resulting in the increased compression strength of the alloys.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.