Effect of heat treatment and ageing on microstructure for hypoeutectic Al-7Si alloy and hybrid metal matrix composites

Abstract

In the present investigation on fabrication and microstructure of aluminium based hybrid composites. A356 based aluminium matrix material with varying reinforcement percentage from 0 to 9 wt. % in steps of 3 wt. % silicon carbide (SiCp) and fixed quantity of 3 wt. % of graphite (Gr) particles were used in fabrication. The specimens were fabricated by stir-cast method. Heat treatment was carried out for the cast specimen at 540oC for 12 hours and further ageing was carried out at 155ºC for 3, 6, 9 and 12 hours durations. The specimen after heat treatment and ageing were quenched in water at 60oC. The prepared specimens (ascast and aged) were examined using optical microscope to know the particle distribution in the matrix. Hardness and tensile were carried out for as-cast and aged specimen. The results were compared with as-cast and aged specimens. There was a significant improvement in hardness and tensile properties due to increase in the weight percentage of SiCp. The specimen A356-9SiCp-3Gr aged at 9 hrs showed improved hardness, and tensile when compared to other tested specimen. The presence of reinforcements (SiCp and Gr) significantly affects the solid state transition kinetics that improves the properties of composites. The presences of reinforcements in the specimens are evident from the electron dispersive spectroscopy (EDS) analysis.