Mechanical behaviour and microstructure evolution of superplastic Mg-8.4 wt pct Li alloy and effect of grain size and phase ratio on its elongation

Mechanical properties and microstructure evolution of Mg-8.4 wt pet Li allo y have been investigated. The superplastic elongation-to-failure 920% at 57 3 K and initial strain rate of 5 x 10(-4) s(-1) at low nominal stress 2 MPa has been demonstrated. It was shown through optical microstructure that th e average grain sizes at gauge length section before and after superplastic tension and at grip section were 7.5 mu m, 31.7 mu m and 20 mu m respectiv ely, indicating significant deformation induced grain growth and static gra in growth. Comparison of experiment data with published data for superplast ic Mg-Li alloys shows that fine grain size and about 50 to 50 phase ratio c ontribute to achieving the largest superplasticity. Some related research w orks in other alloys are compiled and further evidences to such theoretic a rgument are provided.