Microstructures and phase compositions of as-cast and extruded Mg-6Zn-xCa（x=0

1

.35）alloys were investigated by optical microscopy（OM）

scanning electron microscopy（SEM）

X-ray diffraction（XRD）

and the tensile mechanical properties were tested at ambient temperature.The results show that as-cast microstructure is refined and Mg6 Zn3 Ca2 new phase is increased gradually with increasing in Ca content

while MgZn2 phase is decreased gradually until to disappear completely.The second phase tends to distribute along grain boundary with continuous reticulation.Extruded microstructure is refined obviously

where the average grain size is decreased from 15μm for Mg-6Zn alloy to 10μm for Mg-6Zn-0.47Ca alloy.With increasing in the Ca content

tensile strength

yield strength and elongation are firstly increased from 154MPa

67MPa and 6.5%for as-cast Mg-6Zn alloy to 230MPa

78MPa and 13%for as-cast Mg-6Zn-0.085Ca alloy

respectively

and then decreased gradually.Mechanical properties of the alloy is enhanced obviously with 0.085% Ca addition

where the tensile strength and yield strength are decreased lightly

while elongation is increased.However

mechanical properties are deteriorated significantly with more content of Ca（0.47%）addition.