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 ( 2 0 1) 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.