Elevated aging precipitation behaviors of permanent mould and sand mold casting Mg-Gd-Y-Zr alloys were observed by OM（optical microscope）

SEM（scanning electron microscope） and XRD（X-ray diffraction）.The results show that the T4 alloy aged at elevated temperatures is composed of α-Mg solid solution with（Gd+Y） phase and cuboidal particle and a little spheroidized Zr nuclei as well as β phase.Average grain size in the T4 alloy is nearly independent of the elevated aging treatment processes

however

with increasing in aging temperature and in aging time

hardness of the alloy is slowly decreased.In addition

the β phase distributed in trigonal and parallel orientation in the grain can be observed

and precipitates-free zone（PFZ） appears in the grain boundary.Distribution and orientation of precipitates in the alloy at elevated aging is independent of the forming conditions.