The ductility of Mg alloys was limited due to a shortage of independent slip systems. In particular, c-axis compression could not be accommodated by any of the easy slip or twinning modes. Basal-textured samples of pure Mg and Mg-15at%Li were examined for the presence of <c+a> dislocations by post-mortem transmission electron microscopy after small deformations, which forced the majority of grains to compress nearly parallel to their c-axes. A higher density and more uniform distribution of <c+a> dislocations was found in the Li-containing alloy. Because the 1/3<1¯1▪3>{11▪¯2} pyramidal slip mode offers five independent slip systems, it provided a satisfying explanation for the enhanced ductility of α-solid solution Mg-Li alloys as compared to pure Mg. The issue of <c+a> dislocation dissociation and decomposition remains open from an experimental point of view. Theoretically, the most feasible configuration was a collinear dissociation into two ½<c+a> partial dislocations, with an intervening stacking fault on the glide plane. It was speculated that Li additions may lower the fault's energy and, thereby, increased the stability of this glissile configuration.

Transmission Electron Microscopy Investigation of <c+a> Dislocations in Mg and α-Solid Solution Mg-Li Alloys. S.R.Agnew, J.A.Horton, M.H.Yoo: Metallurgical and Materials Transactions A, 2002, 33[3A], 851-8