Growth of Mg2Si crystals shaped by {100} and {111} facets from Al–Mg–Si melts in the presence of calcium.

In this work, primary Mg2Si crystals shaped by {100} and {111} facets were successfully fabricated in Al–Mg–Si melts via the adsorption and poisoning of the Ca element. The modifier Ca plays an important role in determining the morphologies of primary Mg2Si, which can be transformed from dendrites (0 wt%) to crystals with a combination of eight {111} and four {100} facets (0.08 wt%), then to truncated cubes (0.1 wt%), and finally to cubes fully bounded by {100} facets (0.2 wt%) with increasing Ca content. The growth processes of cubic primary Mg2Si have been revealed. As the growth rates of {100} surfaces are diminished by adsorption of the Ca element, primary Mg2Si tends to form perfect cubes with exposed {100} facets. Moreover, by prudently adjusting the concentration of the Ca element, complex polyhedral crystals enclosed by {111} and {100} surfaces were designed and prepared. The results offer valuable insights into designing the modification effect of different modifying elements, which are critical to promoting the industrial application of light alloys with improved morphology and refined size of microstructures. [ABSTRACT FROM AUTHOR]