Anomalous α -Mg Dendrite Growth During Directional Solidification of a Mg-Zn Alloy

Dendritic morphology was investigated in a directionally solidified magnesium-zinc alloy using synchrotron X-ray tomography and electron backscattered diffraction. Unexpectedly, primary dendrites grew along ⟨2131 ⟩ , rather than the previously reported ⟨ 112 0⟩ and ⟨ 2245 ⟩ directions. Further, seven asymmetric sets of side branches formed, instead of six-fold symmetric arms, evolving with three coexisting morphologies per trunk of: traditional, seaweed structure, and free growth. The anomalous growth is attributed to the imposed thermal gradient and zinc-induced interfacial energy anisotropy variations.