Microstructure and Properties of Secondary Al-12%Si Alloy Rapidly Quenched from the Melt

In this study, the effect of rapid quenching from the melt is investigated on the solidification microstructure and tensile properties of a secondary Al-12%Si alloy, which was cast in ingots measuring 45 mm in diameter and 200 mm in height. Compared with conventional casting into metallic molds, significant refinement of all the microstructural constituents was observed under the effect of rapid quenching, including primary alpha-Al, primary silicon, the eutectic and iron-rich intermetallics. The coarse plate-like to fine fibrous transition of eutectic silicon, and the change of coarse plate and needle-shaped iron-rich intermetallic phase particles to a well-dispersed morphology accompanied the microstructure refinement. Both the microstructure refinement and the favorable morphological changes of the phases resulted in the enhanced of tensile properties and more ductile fracture behavior of the alloy. T2 heat treatment additionally increases elongation of the rapidly quenched alloy.