Correlation between crystallographic anisotropy and dendritic orientation selection of binary magnesium alloys

Both synchrotron X-ray tomography and EBSD characterization revealed that the preferred growth directions of magnesium alloy dendrite change as the type and amount of solute elements. Such growth behavior was further investigated by evaluating the orientation-dependent surface energy and the subsequent crystallographic anisotropy via ab-initio calculations based on density functional theory and hcp lattice structure. It was found that for most binary magnesium alloys, the preferred growth direction of the alpha-Mg dendrite in the basal plane is always < 11 (2) over bar0 >, and independent on either the type or concentration of the additional elements. In non-basal planes, however, the preferred growth direction is highly dependent on the solute concentration. In particular, for Mg-Al alloys, this direction changes from < 11 (2) over bar3 > to < 22 (4) over bar5 > as the Al-concentration increased, and for Mg-Zn alloys, this direction changes from < 11 (2) over bar3 > to < 22 (4) over bar5 > or < 11 (2) over bar2 > as the Zn-content varied. Our results provide a better understanding on the dendritic orientation selection and morphology transition of magnesium alloys at the atomic level.