Effect of Sc addition and T6 aging treatment on the microstructure modification and mechanical properties of A356 alloy

Effect of Sc addition and T6 aging treatment on the secondary dendritic arm spacing (SDAS), modification of eutectic Si morphology, β-Al5FeSiand π-Al8Mg3Si6Fe1 phases and its effect on mechanical properties in A356 alloy has been investigated. Addition of 0.4 wt%Sc in A356 alloy resulted in a 50%reduction in the secondary dendritic arm spacing (SDAS). Sc addition changed the morphology of eutectic Si from plate like to fibrous and globular. The needle like morphology of β-Al5FeSi phase in A356 alloy changed to Al5Fe(Si,Sc) phase having smaller size and irregular morphology. Transmission electron microscopy (TEM) diffraction pattern and Energy dispersive spectroscopy (EDS) analysis revealed the presence of β-Al5FeSiand π-Al8Mg3Si6Fe1 phases in A356 alloy which changed to β-Al5Fe(Si,Sc), π-Al8Mg3(Si,Sc)6Fe1 and additional V-AlSi2Sc2phase was observed in Sc containing alloys. Addition of 0.4 wt%Sc to A356 alloy improved its Vickers hardness, Ultimate tensile strength (UTS), Yield strength (YS) and ductility by 20%, 25%, 20% and 30% respectively. Artificial aging treatment resulted in significant improvement in the tensile properties for both A356 and Sc added A356 alloys.