Microstructure and mechanical properties of as-cast and T6 treated Sc modified A356-5TiB2in-situ composite

Abstract

The present article presents the effect of Sc addition on the secondary dendritic arm spacing, eutectic Si modification, intermetallic phase modification, aging behavior and subsequently the mechanical behavior in A356-5TiB2in-situ composite. The A356-5TiB2in-situ composite showed a 40% reduction in SDAS compared with A356 alloy, whereas addition of 0.4 wt% Sc and 5 wt% TiB2 in A356 alloy resulted in a 65% reduction in SDAS. The eutectic Si in A356-5TiB2 composite had a plate like morphology similar to A356 alloy but showed a reduction in length, whereas the addition of Sc resulted in a fibrous and particulate morphology of eutectic Si. The needle like β-Al5FeSi phase in A356-5TiB2 composite changed to Al5Fe(Si,Sc) phase having smaller size and irregular morphology with the addition of Sc. The intermetallic phase formation and phase modification was confirmed and characterized using X-ray diffraction, Transmission electron microscopy - Energy dispersive spectroscopy and Scanning electron microscopy. Addition of Sc to A356-5TiB2in-situ composite resulted in improved mechanical properties. Further, T6 heat treatment revealed a significant improvement in mechanical properties for A356-5TiB2in-situ composite with and without Sc addition.