TEM analysis and related mechanical characterization of age hardened aluminium 7075-grey cast iron particle reinforced composites

Abstract

The aim of the present research work is to improve the hardness-related properties by the combined effect of precipitation of secondary phases through aging treatment and dispersion strengthening. In this study, reinforcement material was cast in the form of rods as per the required composition. Turning operation was performed to convert them into chips using conventional lathe machine. Ball milling setup comprising hardened steel balls was then utilized to pulverize these grey cast iron (GCI) chips to obtain reinforcement particulates. Al 7075-based composites are manufactured with GCI reinforcements by two-step stir casting method. Precipitation hardening treatment is imparted to alloy and composites to enhance the mechanical properties. Hardness and tensile properties are analysed in both as-cast and age hardened conditions. Brinell hardness tester was employed for measurement of hardness. Composites reinforced with GCI particulates significant increase in hardness in comparison with base alloy. 80–100% increase in peak hardness aged at 200°C and 120–140% increase in peak hardness aged at 100°C observed for Al 7075-GCI compared with base alloy. The analysis of tensile behaviour was carried out in electronic tensometer. Ultimate tensile strength increased with the increase in weight percentage of reinforcements. An increase of 40–50% in UTS at peak aged condition obtained at 200°C and 60–70% in peak aged condition at 100°C for Al 7075-GCI composites compared with as-cast composites. Uniformity in reinforcement particle distribution in the matrix is confirmed by the SEM analysis of the composite. TEM analysis of as cast and aged alloy/composites reveal the precipitate size, shape and its dispersion in the matrix phase. Aging kinetics is accelerated by the increase in wt.% of reinforcement.