Solidification Behaviour of Unmodified and SR-Modified Eutectic Si in Binary Al-6si and A319 Al Alloys Using In-Situ Neutron Diffraction

Abstract

Hypoeutectic Al-Si alloys contain coarse, acicular Si plates. This phase is detrimental to the alloy's mechanical properties, since the phase is brittle and the tips of the silicon needles promote stress concentration. However, it is possible to modify the eutectic silicon to have a fine fibrous structure, most commonly by adding trace amounts of Sr, to improve elongation, strength, and thermal conductivity. In this study, in-situ neutron diffraction was conducted during the solidification of unmodified and Sr-modified binary Al-6 wt.% Si and industrial A319 Al alloy to obtain a novel view of the modification mechanism.