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

Abstract 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 〈 1 1 2 ¯ 0 〉 directions in the { 0 0 0 1 } basal plane and twelve along 〈 1 1 2 ¯ 3 〉 directions in the non-basal plane. The 〈 1 1 2 ¯ 0 〉 -oriented branches had secondary arms in four directions with two in 〈 1 1 2 ¯ 0 〉 and two in 〈 1 1 2 ¯ 3 〉 , whereas the 〈 1 1 2 ¯ 3 〉 -oriented branches had secondary arms in three directions with one in 〈 1 1 2 ¯ 0 〉 and two in 〈 1 1 2 ¯ 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.