Effect of additional solute elements (X= Al, Ca, Y, Ba, Sn, Gd and Zn) on crystallographic anisotropy during the dendritic growth of magnesium alloys

Based on the first-principles calculations and crystallographic anisotropy analysis, the effect of additional solute elements on the dendritic growth behavior of binary Mg-X (X = Al, Ca, Y, Ba, Sn, Gd and Zn) alloys are investigated in terms of the orientation-dependent surface energy. The preferred growth direction of the α-Mg dendrite is found to be dependent on the magnitude of the anisotropic surface energy and the difference of crystallographic anisotropy between the matrix Mg and the additional solute X. The most densely packed crystallographic planes are found to be the energetically favorable planes with the minimum surface energy, as exemplified by the {111} plane of Al with fcc (face-centered cubic) structure, the {110} plane of Ba with bcc (body-centered cubic) structure, and the {0001} plane of Y with hcp (hexagonal-close packed) structure. For all additional solute elements studied, Zn exhibits the maximum anisotropy and the according effect on the growth behavior of the α-Mg dendrite is the most significant, which could also be reflected by the complex growth patterns of the Mg-Zn alloy dendrite observed in experiments. Compared with Zn, the crystallographic anisotropy of the other additional solutes is weaker, and their effect on the α-Mg dendrite growth is not as significant as Zn, which is reflected by their similar eighteen-primary branch dendritic morphology in 3D.