Effects of RE erbium on microstructure and mechanical properties of permanent mold casting ZA73 alloy were investigated by OM（optical microscope）

SEM（scanning electron microscope）

EDS（energy dispersive spectrum）and tensile testing.The results indicate that semi-continuous distributed eutectic compound [τ（Mg32（Al

Zn）49）] is converted into discontinuous globular particle on boundary with minor erbium addition

meanwhile

fine Er-Al phase in the alloy can be identified.Tensile testing reveals that with increasing in erbium content

the tensile strength is improved and elongation reachs a peak value with 0.4% Er addition at 200℃.Elevated tensile strength is firstly increased and then decreased with increasing in temperature

in which the maximum value of tensile strength can be obtained at 150℃.