Mechanical properties and machining of aluminum-silicon alloys modified by bismuth or tin

The dry machining performance, microstructure and mechanical properties of hypoeutectic and hypereutectic Al-Si alloys modified with different amounts of Bi and Sn, and cast at different cooling rates, were studied. The measured cutting and thrust forces decreased with the addition of Bi and Sn. These elements caused intense shear localization, and promoted the formation of segmented chips, thereby improving the dry machining performance. Also Bi and Sn melted and thus acted as lubricants during dry turning. However, the mechanical properties decreased with the addition of Sn, although Sn had no effect on the Si morphology. Bi had no effect on the Si morphology when cast at high cooling rates. The optimum amount of Bi addition was found to be 0.5 % and this alloy cast under a high cooling rates of 26 °C/s, improved the overall machining performance without compromising the mechanical properties