Abstract: Aging behavior of Mg-3.6Y-0.5Zr and Mg-2.7Nd-0.5Zr alloys was investigated by microhardness measurement and transmission electron microscopy. In the case of Mg-Y-Zr alloy, the presence of β″ phase, a major strengthener, having base centered orthorhombic structure with its lattice constants of aβ″=0.64 nm, bβ″=2.22 nm, and cβ″=0.52 nm was identified. In the case of Mg-Nd-Zr alloy aged at 250℃, the presence of β″ and β′ phases was identified. The crystal structure of β″ phase was found to be DO19 and its orientation relationships with Mg matrix were [0001] β″//[0001]Mg and [01 0] β″//[01 0]Mg. The β′ phase had face centered cubic structure and its orientation relationships with Mg matrix were [011] β′//[0001]Mg and [ 1 ]β′//[ 110]Mg. The Mg-2.7Nd-0.5Zr alloy showed higher hardness compared with Mg-3.6Y-0.5Zr alloy.

Key words: Mg-Y-Zr alloy, Mg-Nd-Zr alloy, Precipitation sequence