Flow and cavitation in a quasi-superplastic two-phase magnesium-lithium alloy

Tensile tests were conducted at temperatures from 473 to 623 K on a two-phase Mg-9.5 wt.% Li-1.0 wt.% Zn alloy with an initial lamellar structure. It is shown that the alloy exhibits a quasi-superplastic behavior with a maximum recorded elongation of 290% at 523 K when testing with an initial strain rate of 1.0 x 10(-4) s(-1). The experiments give a strain rate sensitivity of similar to 0.33 and an activation energy of similar to 2kJ mol(-1). Metallographic inspection after failure revealed the occurrence of extensive internal cavitation and quantitative measurements were undertaken to determine the shapes and sizes of these internal cavities at two different testing temperatures. It is shown that the results suggest a transition with increasing strain from cavity growth by diffusion to growth controlled by plastic flow in the surrounding crystalline matrix. (c) 2006 Elsevier B.V. All rights reserved.