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 pct Li alloy have been investigated. The superplastic elongation-to-failure 920% at 573 K and initial strain rate of 5 * 10^-4 s^-1 at low nominal stress 2 MPa has been demonstrated. It was shown through optical microstructure that the 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 respectively, indicating significant deformation induced grain growth and static grain growth. Comparison of experiment data with published data for superplastic Mg-Li alloys shows that fine grain size and about 50 to 50 phase ratio contribute to achieving the largest superplasticity. Some related research works in other alloys are compiled and further evidences to such theoretic argument are provided,