Characterisation of the 3-D dendrite morphology of magnesium alloys using synchrotron X-ray tomography and 3-D phase-field modelling

The 3-D morphology of α-Mg dendrites for Mg−30 wt.% Sn and Mg−30 wt.% Gd alloys was investigated and characterised using the synchrotron X-ray tomography technique. Results show that the α-Mg dendrites had eighteen primary branches with six growing along 〈112¯0〉 directions in the {0001} basal plane and twelve along 〈112¯3〉 directions in the non-basal plane. The 〈112¯0〉-oriented branches had secondary arms in four directions with two in 〈112¯0〉 and two in 〈112¯3〉, whereas the 〈112¯3〉-oriented branches had secondary arms in three directions with one in 〈112¯0〉 and two in 〈112¯3〉. By combining and modifying certain terms of spherical harmonics, an anisotropy growth function was developed for the first time to describe the growth of an eighteen-branch α-Mg dendrite. The 3-D phase field simulations were then performed and great agreement was achieved between the simulation results and experiment on various key growth aspects including dendrite morphology and side-branching patterns.