Mechanical Behavior And Its Strain Rate Effect Of Mg-Li Alloys

Plastic instability, as known the serrated flow or PLC effect, occurring during tensile and compression tests in the single-phase Mg-4Li, Mg-4Li-1Al and Mg-4Li-1Y-6Zn alloys have been investigated. However, there has no PLC phenomenon to be occurred for the double-phase Mg-6Li-1Al and Mg-6Li-1Y-6Zn alloys at the same testing conditions. It is found that the PLC effect is enhanced with increasing addition of Al, Y and Zn, and the phenomenon occurs always at a given strain, called as the critical strain. The critical strain values increase with increasing the strain rate for both alloys of Mg-4Li, Mg-4Li-1Al, but appears to be the V-type in shape for the alloy of Mg-4Li-1Y-6Zn, and the strength of this alloy decreases with the increasing in the strain rate, the strain rate sensitive index appears always to be negative.The microstructural evolution of the Mg-Li alloys subjected to different strain rates has been characterized by SEM, EBSD and TEM. The results show that the solution strengthening effect of the alloys is weak due to the low level of Al addition. However with the additions of Y and Zn elements, the grains are refined, and the quasi-crystalline phases: I-phase and W-phase, occur in both alloys of Mg-4Li and Mg-6Li, which lead to the strengthening of the alloys further.The twinning of both Mg-4Li and Mg-6Li alloys become more obvious due to the addition of Al, and the amount of the twins increase with the increase in strain rate, but the twins are hardly observed just after addition of Y and Zn into the alloys. TEM observations show that the twins always appear in the deformed structure whether the PLC effect occurs in the alloy or not, meaning that the DSA is responsible for PLC effect for this kind of alloys.