Microstructure modification and quasicrystalline phase formation in Al-Mn-Si-Be cast alloys

Abstract

In this paper, we report the formation of the new quaternary icosahedral quasicrystal in the Al-Mn-Si-Be system, which has a primitive icosahedral structure and has a significant lower cooling rate at the time of its formation. The icosahedral quasicrystalline phase was found to form in the Al-rich composition of Al-Mn-Si-Be alloy by conventional casting technique as well as by rapid quenching technique, indicating that the addition of Be to Al-Mn-Si alloys improves the quasicrystal forming ability. The icosahedral phase in conventionally cast Al-Mn-Si-Be alloys forms as a dendritic phase in the under-cooled melt showing five well-developed branches indicating the five-fold symmetry structure. At the later stage of the growth of the icosahedral phase, 1/1 approximant phase forms heterogeneously from the icosahedral phase. The Al-Mn-Si-Be icosahedral phase is metastable, and transforms into the 1/1 cubic approximant phase at high temperature. (C) 2003 Elsevier B.V. All rights reserved.