Influence of Mg on Micro-Mechanical Behaviour of as Cast Al–Mg System

Abstract

In the present work, a study was carried out for various possible Mg concentrations in order to optimize Mg amount in Al–Mg system as far as metallurgical and mechanical properties are concerned. In molten Al, variations of amount of Mg were made from 0.05–7 wt % Mg using a resistance heating furnace. Intermetallics like Al–Mg, Mg–Si, Al–Si, etc.,—were formed at processing temperature. During solidification, these intermetallics were pushed towards the grain boundaries and formed clusters, which was studied using SEM–EDS analysis. Heavier phases revealed as dark regions whereas lighter phases as less dark or bright regions. Due to such pushing effects of intermetallics during solidifications of bath in metallic die, development of grain boundaries started in the form of remarkable thickening of it into the Al matrix. This phenomenon was found to be more pronounced, as the Mg concentration was increased. Hence, in case of 7 wt % Mg, it was found that maximum amount of intermetallics gathered at grain boundaries. Segregation tendencies of various intermetallics and excess free Mg were found non uniform for a higher range of Mg. Ultimate tensile strength, specific strength, and hardness properties were studied and they were found to be highest in Al–3 wt % Mg system along with low density and ductility values. Therefore, in the present study, 3 wt % Mg is considered to be an optimum level of Mg concentration based on its micro-mechanical behaviour.