Crystallographic and Experimental Disproof of Pyramidal Slip in Magnesium

The activation of non-basal pyramidal slip has been perceived as key to enhance the ductility of magnesium and its alloys. However, there has never been convincing evidence to show the physical existence of dislocations and their involvement in deformation has been a core issue in magnesium research. In the present work, the impossibility of slip is analyzed based on fundamental concepts of dislocation and atomic interactions. The atomic configurations and crystallographic features in association with dislocations are unambiguously revealed for the first time, demonstrating that any possible dislocation core structures would involve too many atoms on multiple lattice planes and are physically impossible. Experiments of magnesium single crystal compression along its c-axis were conducted at temperatures from 20°C to 500°C and the results showed no evidence of the involvement of dislocations in any form as a mechanism of deformation during either plastic flow or fracture. von Mises criterion for compatible deformation, which drives the pursuit of pyramidal slip, is critically discussed.