Comparing the roles of Sb and Bi on microstructures and application properties of the Al-15% Si alloy

Abstract

The roles of Bismuth (Bi) and Antimony (Sb) additions to hypereutectic Al-Si alloys with significant variation in solidification cooling rates have yet to be unraveled. Both elements are considered of importance in the production chain of Al-based metallurgical products: while Sb is a refiner of the eutectic Si, Bi remains important in applications requiring better levels of alloy machinability. Based on these verified realities, the present research aims to modify the Al-15 wt% Si hypereutectic alloy with 1.0 wt% Bi as well as with 1.0 wt% Sb. The implications of these incorporations on the characteristics of the microstructure phases and the tensile/wear properties are examined. Various samples characterized by distinct solidification rates have been generated through transient directional solidification experiments. Several methods were used to examine and compare the two alloys with each other: microstructure and segregation are investigated by CALPHAD simulations, optical microscopy, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), whereas wear and tensile properties have been determined through standardized measurements. While adding Sb provides the growth of broken Si in the form of lamellae and some fraction of fibers for higher solidification rates, Bi alloying preserves lamellar growth for all rates examined. Adding Bi is better than Sb in reaching higher tensile properties, but Sb presence provides greater wear resistance. Both alloying elements ductilize the brittle Al-15 wt% Si alloy.