EFFECT OF INTERRUPTED QUENCHING ON HARDNESS, TENSILE STRENGTH AND MICROSTRUCTURES OF AL-SI-MG/10% LOCUST BEAN WASTE ASH COMPOSIT

Abstract

This study investigates the potentials of Neem(AzadirachtaIndica) seed oil as quenchant for precipitation hardening of Al-Si-Mg/10% locust bean waste ash composite. This was with a view to improving the precipitation response leading to smaller grain size of the Al-Si-Mg/locust bean waste ash composite. The composite consists of a matrix of Al–Si–Mg and the locust bean waste ash particulates as reinforcement. The composite material was then subjected to thermal treatment through solution heat treatment at 540oC, soaked for 1 hour and then quenched simultaneously in neem seed oil and water at 30oC. Some of the quenched samples were delayed for 0.02hr, 0.5hr, 1hr, 1½hr 2hrs and 3hrs respectively and then age hardened at 180oC for 2 hours, followed by air cooling in order to evaluate the properties as well as the resulting microstructures. The mechanical properties of the composites examined include the hardness and the tensile strength.The microstructures of the heat-treated composite were also examined using OPM and SEM while the phases developed were revealed using XRD. The results of the microstructures of the composite show a uniform dispersion of the reinforcement along the grain boundaries of the alloy. The results show that the composite with the intermediate natural ageing time of 3hrs has the highest properties in both quenchants. The hardness value and tensile strength in neem seed oil and water are 29.2HRF & 28.1HRF, 2.58 & 2.3kN/mm2 respectively, which corresponds to 93.4% & 86.1%, 207% & 173.8% incrementin hardness and tensile strength. Within the α-aluminium solid solution, the phases are indicated by XRD with Mg2Si, Mg2Mn, Al12Mg17, SiAl and Al8Mg3FeSi6 intermetallic compounds being formed. Thus, these confirmed the SEM and OPM microstructure examined which can be said to be present in the thermally treated composite leading to improved properties. From these results, it can be concluded that the locust bean waste ash particulates can be used to enhance the properties of Al–Si–Mg alloy using indigenously sourced quenchant for engineering applications.