Substructure induced dendrite-fragmentation during thermomechanical processing of as-cast Mg-Sn-Li-Zn alloy

Abstract The present work deals with emphasizing the role of substructure development in fragmentation of the cast structure in Mg-Sn-0.3Li-3Zn alloy during thermomechanical processing. In this respect, a new micro-mechanism and a conceptual model were proposed for dendrite fragmentation, which was supported by 3D-tomography, electron back scattered diffraction, and angle selective back-scattered imaging analyses. Balancing of the dihedral angle of the non-equilibrium triple junctions led to the formation of grooves at the dendrite arms, followed by penetration of α-Mg matrix through the grooves and finally resulted in fragmentation of the specified dendrite arm. In fact, despite the conventional expectation regarding the high contribution of brittle fracture and shearing in fragmentation of the dendrites at low temperature regime, it was observed that the substructure development in a medium-to-high stacking fault energy material greatly participated in thermally-activated disintegration of the dendritic cast-structure.