Study of Microstructure Evolution during Semi-Solid Processing of an In-Situ Al Alloy Composite

Abstract

In the present work, effect of pouring temperature (650°C, 655°C, and 660°C) on semi-solid microstructure evolution of in-situ magnesium silicide (Mg₂Si) reinforced aluminum (Al) alloy composite has been studied. The shear force exerted by the cooling slope during gravity driven flow of the melt facilitates the formation of near spherical primary Mg₂Si and primary Al grains. Shear driven melt flow along the cooling slope and grain fragmentation have been identified as the responsible mechanisms for refinement of primary Mg₂Si and Al grains with improved sphericity. Results show that, while flowing down the cooling slope, morphology of primary Mg₂Si and primary Al transformed gradually from coarse dendritic to mixture of near spherical particles, rosettes, and degenerated dendrites. In terms of minimum grain size and maximum sphericity, 650°C has been identified as the ideal pouring temperature for the cooling slope semi-solid processing of present Al alloy composite. Formation of spheroidal grains with homogeneous distribution of reinforcing phase (Mg₂Si) improves the isotropic property of the said composite, which is desirable in most of the engineering applications.

Keywords:

• Cooling slope
• Metal matrix composite
• Primary Al
• Primary Mg₂Si
• Rosette
• Semisolid
• Spheroidal