Effect of Ca and Sr on the grain refinement of the ZA91D Mg alloy was conducted.Although w（Ca）

<

1% addition into AZ91D Mg alloy can refine grain size and increase yield strength

yet decrease the tensile strength and elongation of the alloy due to the segregation of Al

2

Ca phase in grain boundary resulting in embrittlement of the alloy matrix.The grain size can almost remain unchange with the addition of w（Sr）

<

0.2%.The mixed Ca and Sr addition not only reduce the grain size but also improve the comprehensive mechanical properties of the alloy.