Effects of Bi addition on Si features, tensile properties and wear resistance of hypereutectic Al-15Si alloy

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.

The Role of Bismuth as Trace Element on the Solidification Path and Microstructure of Na‐Modified AlSi7Mg Alloys

“…[7][8][9] Bismuth is also used as a chemical refiner for the eutectic silicon flakes in both hypoeutectic and hypereutectic Al-Si alloys resulting in higher tensile and wear resistance performances. [10][11][12][13][14][15] It is known how Bi can counteract, even as a trace element, the effect of further alloying additions or preliminary molten metal treatments affecting the final microstructure and tensile performance of the alloy. Some studies [16,17] stated how the presence of Bi in Sr-modified Al-Si foundry alloys increases the eutectic growth temperature, and a fibrous to the plate-like transition of eutectic Si occurs.…”

“…[ 7–9 ] Bismuth is also used as a chemical refiner for the eutectic silicon flakes in both hypoeutectic and hypereutectic Al–Si alloys resulting in higher tensile and wear resistance performances. [ 10–15 ]…”

Evaluating Microstructure, Wear Resistance and Tensile Properties of Al-Bi(-Cu, -Zn) Alloys for Lightweight Sliding Bearings

“…Pereira et al [26] recently demonstrated that the tensile properties of the Al-15 wt.% Si-1 wt.% Bi alloy are higher than those of the non-modified Al-15 wt.% Si alloy. It is demonstrated that the addition of Bi to hypereutectic Al-Si alloys facilitates improvement in alloy strength.…”