The sequence of intermetallic formation and solidification pathway of an Al-13Mg-7Si-2Cu in-situ composite

Abstract

The phase transformation sequence and solidification behaviour of an Al-13Mg-7Si-2Cu in-situ composite was examined using a combination of computer-aided cooling curve thermal analysis and interrupted quenching techniques. Five different phases were identified by analysing the derivative cooling curves, the X-ray diffraction profile, optical and scanning electron microscopy images and the corresponding energy dispersive spectroscopy. It has been found that the solidification of this alloy begins with primary Mg2Si precipitation and continues with the formation of eutectic Al-Mg2Si, followed by Al5FeSi and simultaneous precipitation of Al5Cu2Mg8Si6 and Al2Cu complex intermetallic phases. The formation of the last three intermetallic compounds changes the solidification behaviour of these composites remarkably due to their complex eutectic formation reactions. The solidification of the alloy, calculated using the Factsage thermochemical analysis software, has demonstrated a good agreement with the experiments in terms of compound prediction, their weight fractions and reaction temperatures.