The Formation and Characterization of the Primary Mg₂Si Dendritic Phase in Hypereutectic Al-Mg₂Si Alloys

抄録

The formation of a primary Mg₂Si dendritic phase in hypereutectic Al-Mg₂Si alloys is investigated using melt-spinning techniques. The results indicate that, at the initial stage, the primary Mg₂Si crystal rapidly grows in a non-faceted manner, forming a smooth dendritic or fluted structure. As the undercooling of the process is varied, the growth behavior transitions from non-faceted to faceted. Subsequently, Mg₂Si crystals grow preferentially along the [100] direction producing growth hillocks and forming stable branches. The morphology of the primary Mg₂Si crystal exhibits angular facets. Furthermore, if V_[100]/V_[111] = √3 , the crystal grows as a perfect octahedral dendrite (the dendrite is composed of octahedrons), and if V_[100]/V_[111] < √3 , the crystal grows with imperfect octahedral subunits. Lastly, the growth process of the primary Mg₂Si dendrites is discussed.