Machinability characteristics, thermal and mechanical properties of Al-Mg2Si in-situ composite with bismuth

In the present work, the effects of Bi addition on machinability, thermal, microstructure and mechanical properties of Al-20Mg2Si in- situ metal matrix composite are investigated. Structure of primary Mg2Si reinforcement particle changed from coarse to fine polygonal accompanied with decrease in size and increase in density. Nucleation temperature of primary Mg2Si and solidification temperature range of Al-20Mg2Si composite decreased after addition of Bi. In addition, Bi additions improved ultimate tensile strength (UTS), elongation (El%), impact toughness and hardness value. Fracture surface of composite with Bi addition showed more fractured than decohered particles which are related to higher El% and impact toughness. Dry turning tests for various cutting conditions (90, 180 and 270 m/min) and feed rates (0.1, 0.015 and 0.2 mm/rev) were carried out with a cemented carbide tool. The result indicated that surface roughness and cutting force decrease with addition of 0.4 wt.% Bi due to change in the Mg2Si particle size from 24 µm to near 10 µm with less built-up edge. Chip breakability of base alloy was superior because of Mg2Si particles. It was also observed that Bi acted a lubricant role during machining process and therefore decreased friction between the cutting tool and particles.