Formation of novel microstructures in conventionally cast Al–Fe–V–Si alloys

Abstract

The present paper reports the formation of novel morphologies of intermetallic compounds during the solidification of different Al–Fe–V–Si alloys using cooling rates ranging from 1 to 20 K s−1. The influence of cooling rate, composition of the alloy and the addition of Mg and Ni–20%Mg alloy on the morphology of the intermetallic phases, particularly that of Al13Fe4 phase, is reported. Al13Fe4 forms with a ten-armed star shaped morphology with small amount of Si (<1 wt.%) at a cooling rate of ≈14 K s−1. A lower cooling rate and higher Si content result in degeneration of the ten-armed stars into other morphologies. The higher the Si content, the higher the cooling rate required to form the ten-armed star-shaped Al13Fe4 phase. Ten-fold growth morphology of the precipitates is formed due to twinning along or (1 0 0) planes. The morphology, size and distribution of those precipitates can be considerably modified by Mg treatment. Treatment of an Al–8.3Fe–0.8V–0.9Si alloy melt with 1.5 wt.% of Mg or 1 wt.% of a Ni–20Mg alloy alters the ten-armed growth morphology to rectangular, hexagonal or other compact forms.