Microstructural analysis of modification and grain refinement in a hypoeutectic Al-Si alloy

It is well known that in hypoeutectic Al-Si alloys addition of titanium boride refines primary aluminium and addition of strontium modifies eutectic silicon. In this work their individual and simultaneous effect on both features has been investigated quantitatively. On the basis of experimental observations and quantitative analysis, it was concluded that an addition of 0.002 wt-% titanium almost halves grain size of primary aluminium in an ingot of A356, cast in a bar-shaped copper mould. Combining 0.002 wt-% titanium (as Al-3Ti-B) with 0.02 wt-% strontium resulted in a decrease in this grain refinement. However, an addition of 0.02 wt-% strontium has a slight refinement effect on primary aluminium phase. In order to quantify the effect of addition on eutectic silicon readily, as-cast specimens were heat-treated. It was observed that the number of eutectic silicon particles in Sr-modified specimens increased in a higher level compared to a Sr+Ti treated specimen. It was also found that Ti slightly influences the size of eutectic silicon particles.