High strength Mg alloys with self assembled atomic pillar nanoprecipitates

1. High strength Mg alloys with self assembled atomic pillar nanoprecipitates Zi-Kui Liu, Pennsylvania State Univ University Park, DMR 1006557 Since the main challenges in developing Mg alloys are to increase their strength, ductility, as well as stability at high temperatures, it is crucial to understand the fundamental properties which affect their mechanical properties. Formation of stacking faults is fundamental in deformation of materials with hcp structure such as Mg and Ti alloys, affecting core structures and the mobility of dislocations, twinnability and ductility, and creep rate. In this work, (i) the electron localization morphologies of growth (I1), deformation (I2) and extrinsic (EF) fault of HCP Mg are determined, yielding quantitative descriptions of charge transfer between atoms in and out of the stacking faults. (ii) effect of 17 alloying elements on the stacking fault energy in binary Mg-X alloys is investigated in views of crystallography and electron localization morphology. The rod-like directional bonds in regular planes have transformed into homogeneous tetrahedral particles in fault planes, which are strengthened by alloying HCP and FCC elements but weakened by alloying BCC. (iii) it is proposed that formation of self assembled atomic pillar nanoprecipitates in long period stacking orders (LPSO) of Mg-X-Yalloys is one important strengthen mechanism enhancing the mechanical properties. (ii) (i) (iii) I1 I2 HCP Mg EF LPSO Mg97X2Y1 Mg-X