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

Abstract

The formation of a primary Mg 2 Si dendritic phase in hypereutectic Al-Mg 2 Si alloys is investigated using melt-spinning techniques. The results indicate that, at the initial stage, the primary Mg 2 Si 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, Mg 2 Si crystals grow preferentially along the [100] direction producing growth hillocks and forming stable branches. The morphology of the primary Mg 2 Si crystal exhibits angular facets. Furthermore, if V ½100 =V ½111 ¼ ffiffi ffi 3 p , the crystal grows as a perfect octahedral dendrite (the dendrite is composed of octahedrons), and if V ½100 =V ½111 < ffiffi ffi 3 p , the crystal grows with imperfect octahedral subunits. Lastly, the growth process of the primary Mg 2 Si dendrites is discussed.

Microstructural Improvement of Eutectic Al + Mg2Si Phases on Al–Zn–Si–Mg Cast Alloy with TiB2 Particles Additions

“…In Al–Si–Mg alloy systems, Mg 2 Si phases are crystallized according to the ratio of Si and Mg composition. In as-cast conditions, Mg 2 Si phases grow in a coarse dendritic shape [ 3 , 4 , 5 , 6 ]. Coarse dendritic Mg 2 Si phases lead to nonhomogeneous stress concentration and reduce the mechanical properties of Al alloys.…”

Effects of Sr+Ce on Microstructure and Abrasive Resistance of <i>In-Situ</i> Mg₂Si/Al-Si-Cu Composites

“…The various conventional ex situ processes of fabricating aluminum MMCs possess some inherent defects, such as residual microporosity, uneven distribution of reinforcement, non-wetting of the reinforcement, control of matrix-reinforcement interface, scaling up of the process for industrial utilization and processing cost 1,2) . The in situ prepared MMCs have been widely explored in an effort to engineer an interfacial structure by achieving compatible interfaces between matrix and reinforcement [3][4][5] . In-situ Mg 2 Si/Al-Si-Cu composite has high potential as a wear resistant material because an intermetallic compound of Mg 2 Si exhibits the high melting temperature, low density, high hardness, low thermal expansion coef cient 6) and the potential for cost reduction as well.…”