No abstract

Al-Si alloys are very important in the automotive industry. This is thanks to their high strength to weight ratio, suitable fluidity, good corrosion resistance and high productivity. The shape of the eutectic Silicon (Si) has been widely studied since it is considered an index of quality regarding many application properties. Understanding the effects of alloy additions on the morphology of Si has drawn researcher’s attention. One of these elements of interest is Bismuth (Bi), which may be part of the composition of Al-Si alloys either as an addictive or a contamination. Hence, the microstructure aspects related to the presence of Bi are important requiring further consideration. In the present study, Al-15wt% Si hypereutectic alloy is modified with 1.0 wt% Bi. The goal is to compare the effect of this addition on the morphology of the phases forming the microstructure and on tensile/wear properties. In order to pursue that comparison, previously available data for the binary Al-15wt% Si alloy will be used. Various samples characterized by distinct cooling rates were generated by transient directional solidification of the ternary Al-Si-Bi alloy. The experimental variations of the eutectic spacing will be compared to each other based on their trends. It was found that the addition of minor Bi content (∼1%) permitted tensile strength and ductility of 195 MPa and 14%. Furthermore, wear resistance was improved thanks to Bi. The reasons for that will be outlined.

Bismuth (Bi) alloying in Aluminum (Al) alloys is considered of importance in special applications requiring improvements in the alloy machining. Despite that, the influence of Bi either on evolution of the solidification or on resulting microstructure of hypereutectic Al-Si alloys is still to be determined. The present research work is devoted to these requirements. In the present study, Al-15wt.% Si hypereutectic alloy is modified with 1.0 wt.% Bi. The effects of this addition on the morphology of the phases forming the microstructure and on the tensile/wear properties are investigated. Various samples characterized by distinct cooling rates are generated by transient directional solidification of the ternary Al-Si-Bi alloy. Microstructure is examined by optical microscopy and scanning electron microscopy (SEM) analyses, segregation by energy-dispersive X-ray spectroscopy (EDS) whereas wear and tensile properties have been characterized by standardized tests. The experimental variations of the eutectic spacing are compared to each other based on their trends. It is found that the addition of minor Bi content (~1 wt. %) permitted tensile strength and ductility of 195 MPa and 14%. Furthermore, wear resistance is improved by up to 20% due to the Bi addition. The reasons for that will be outlined.