Effect of Li content on the indentation creep characteristics of cast Mg-Li-Zn alloys

Creep behavior of the hcp Mg-4Li-1Zn (LZ41), hcp/bcc Mg-8Li-1Zn (LZ81), and bcc Mg-12Li-1Zn (LZ121) cast alloys was studied by long-term Vickers indentation testing in the temperature range of 423-498 K and under constant load of 5 N. It was established that increasing Li content decreased the creep resistance at all test temperatures. This was stemmed from the effect of Li on the crystal structure of the alloys, the increment of which increased the volume fraction of the bcc beta-phase. This phase activated non-basal slip and facilitated the slip-assisted deformation, and thus, resulted in lower strength and creep resistance. The average stress exponents of about 7.0, 4.5, and 4.2 and activation energies of 90.0, 91.7 and 98.2 kJ/mol were obtained for the LZ41, LZ81, and LZ121 alloys, respectively. It is suggested that the operative creep mechanism is dislocation pipe diffusion in the LZ41 alloy, and pipe-diffusion-controlled dislocation viscous glide in the LZ81 and LZ121 alloys. (C) 2015 Elsevier Ltd. All rights reserved.