Serrated yielding during nanoindentation of thermomechanically processed novel Mg-9Li-7Al-1Sn and Mg-9Li-5Al-3Sn-1Zn alloys

Abstract

In this study, nanoindentation measurements within the hcp α-phase and the bcc β-phase were carried out on two thermomechanically (TM) processed Mg-9Li-7Al-1Sn and Mg-9Li-5Al-3Sn-1Zn alloys to reveal the individual mechanical strength of the phases. Commercially pure Mg and AZ31 Mg alloys were also analysed to study the contribution of alloying addition on the mechanical strength on nano-length scale, such as hardness and elastic modulus of the constituent phases, in Mg-Li alloys. The average hardness and reduced elastic modulus values of TM processed Mg-9Li-7Al-1Sn and Mg-9Li-5Al-3Sn-1Zn measured by nanoindentation were observed to be higher (80% and 30%, respectively) than that of pure Mg. The elastic modulus values of both alloys are about 58 GPa, which is much larger than that of other Mg-based alloys (∼45 GPa). Pop-in events (serrated yielding due to the Portevin-Le Chatelier effect) were also observed in TM processed Mg-9Li-7Al-1Sn and Mg-9Li-5Al-3Sn-1Zn alloys and were quantified using models developed by Taylor and Morris. © 2013 IOP Publishing Ltd.