Microstructural formation in a hypereutectic Mg–Si alloy

In the present work, the microstructure of an ingot metallurgy hypereutectic Mg-8 wt.% Si alloy was studied using electron probe microanalysis (EPMA) and the solidification process was discussed. The components of the alloy are Mg2Si and Mg. The solidified microstructure of the alloy contains three constituents: Mg2Si primary dendrites that are surrounded by Mg sub-primary particles and the Mg–Mg2Si eutectic. The primary Mg2Si dendrites have a secondary dendrite arm spacing d2 of approximately 17 μm or show polygonal morphologies with a mean size of 30 μm. An Mg phase appearing as halos surround the Mg2Si constituents. The Mg–Mg2Si eutectic has a regular morphology of rod-like Mg2Si distributed in a continuous matrix of Mg having an interphase spacing r of approximately 0.8 μm.