Microstructures and high temperature mechanical properties of A356-Mg2Si functionally graded composites in as-cast and artificially aged (T6) conditions

Functionally graded in-situ A356-Mg2Si composites by centrifugal casting method have been studied with varying percentage of extra Mg additions during synthesis. The coarse primary Mg2Si particles and the Si morphology in eutectic do not yield appreciable mechanical properties. Solution treatment and artificial ageing (T6) are effective means to improve mechanical properties by refining the as-cast structure with additional formation of very fine precipitates during ageing. The microstructural evolution has been assessed by optical, scanning and transmission electron microscopy and X-ray diffraction analysis. Ageing curves are plotted with hardness versus ageing time. High temperature tensile properties are evaluated at room temperature, 150 degrees C and 300 degrees C at different layers of the graded composites and are compared between as-cast and T6 conditions. The tensile fracture mechanisms are explained from fractographs. A remarkable improvement in high temperature tensile strength at 150 degrees C with adequate ductility is observed in T6 condition with respect to as-cast condition. (C) 2019 Elsevier B.V. All rights reserved.