The effects of different Y contents on microstructure of ZM5 Mg alloy were investigated by optical microscope and SEM and EPA.It was found that 2[WTXT]%[WT]

Y addition can obviously improve the microstructure of the ZM5 Mg alloy.X ray diffusion and OM observation indicated as-cast microstructure of the alloy consitsts of α-Mg phase and net-like β-Mg

12

Al

17

phase in boundary

in which solid solution treated β-Mg

12

Al

17

phase was dispersed in the matrix

in turn

microstructure of ZM5 alloy containing Re element Y consists of α phase

β-Mg

12

Al

17

phase and particle MgY phase.Solid solution treated alloy consists of MgY phase and precipitated Al

2

Y phase.SEM showed that ZM5 Mg alloy possesses the features of cleavage fracture while ZM5 Mg alloy containing Y has mixed fracture morphology of quasi-cleavage fracture and boundary fracture.The reason is that enhancing phase MgY and dispersely precipitated phase transform the fracture morphology.