In situ X-ray diffraction and crystal plasticity modeling of the deformation behavior of extruded Mg-Li-(Al) alloys: An uncommon tension-compression asymmetry

The effects of alloying additions and grain size on the deformation behavior of two extruded Mg-4 wt.% Li and Mg-4 wt.% Li-1 wt.% Al alloys were studied. To determine the underlying deformation mechanisms, we employed a combination of texture analysis, in situ energy dispersive X-ray synchrotron diffraction and elasto-plastic self-consistent modeling. We show that both alloys exhibit two uncommon features: (1) low tension-compression asymmetry in yield strength and (2) a so-called positive asymmetry in which the compression yield strength is higher than the tension yield strength. Our analyses suggest that this unusual asymmetry arises because the addition of Li hinders the activation of {101¯2}〈101¯1¯〉 tension twinning. We also show that the increases in the yield stress and hardening rate with the addition of Al is a consequence of increases in the resistances to slip but a decrease in the resistance to {101¯2}〈101¯1¯〉 twinning.