Refinement and modification of primary Mg2Si in an Al–20Mg2Si alloy by a combined addition of yttrium and antimony

Abstract

The complex modification of primary Mg₂Si in an Al–20Mg₂Si alloy by simultaneous addition of yttrium (Y) and antimony (Sb) was investigated in the present work. It was found that the combined addition of 0.5 wt% Y–Sb had a more significant modifying effect than the single addition of an equivalent amount of Y or Sb. After modification, coarse Mg₂Si dendrites were changed into fine polyhedra with an average size decreasing from 86 to less than 18 μm. It has been demonstrated that Sb participated in the formation of Mg₃Sb₂, which acts as a heterogeneous nucleus of primary Mg₂Si and hence significantly refines their sizes. Meanwhile, Y could obviously adsorb and poison the preferred growth along the <100> directions of primary Mg₂Si crystals, and hence not only changed their final morphology to a truncated octahedron but also reduced their sizes. Furthermore, the skeleton-type growth process of the truncated octahedral primary Mg₂Si in the Al–20Mg₂Si alloy co-modified by 0.5 wt% Y–Sb was also revealed. Our study provides a new insight into the design of more efficient modifiers by the combined addition of a refiner (e.g. Sb) and a growth inhibitor (e.g. Y), which is critical to tailor new light-weight alloys with high strength and toughness.