Combined effect of bismuth content and cooling rate on microstructure and mechanical properties of Al–8·5Si–0·4Mg–0·3Fe alloy

Abstract

This study investigates the combined effect of Bi content (0?1, 0?2, 0?4 and 0?5 wt-%) and cooling rate (from 0?7 to 4uC s 21 ) on the microstructure, tensile characteristics, quality index and twoparameter Weibull modulus of an Al-8?5Si-0?4Mg-0?3Fe alloy. Results show that Bi refined the eutectic Si structure and that increasing the cooling rate intensified the refining efficiency. The thickness of the b-Al 5 FeSi intermetallic decreased with an increase in the cooling rate, but no significant effect was observed with the addition of Bi. The contour maps of mechanical properties suggest that the effect of cooling rate on mechanical properties was more significant than that of Bi additions. The highest Weibull modulus for the base alloy and Bi containing alloy was obtained at the cooling rate of 4uC s 21 . Decrease in the thickness of b intermetallic phase and reduced porosity with increasing cooling rate appeared to cause a decreased variability of UTS data.Cette é tude examine l'effet combiné de la teneur en Bi (0?1, 0?2, 0?4 et 0?5% en poids) et de la vitesse de refroidissement (de 0?7 à 4uC s 21 ) sur la microstructure, les caracté ristiques de tension, l'index de qualité et deux modules de Weibull d'un alliage d'Al-8?5Si-0?4Mg-0?3Fe. Les ré sultats montrent que le Bi raffine la structure de l'eutectique de Si et que l'augmentation de la vitesse de refroidissement intensifie le rendement du raffinement. L'é paisseur de l'intermé tallique Al 5 FeSi-b diminuait avec une augmentation de la vitesse de refroidissement, mais on n'a pas observé d'effet important avec l'addition de Bi. Les tracé s du contour des proprié tés mé caniques suggèrent que l'effet de la vitesse de refroidissement sur les proprié té s mé caniques é tait plus important que celui des additions de Bi. On a obtenu le module de Weibull le plus é levé pour l'alliage de base et pour l'alliage contenant du Bi à la vitesse de refroidissement de 4uC s 21 . La diminution de l'é paisseur de la phase intermé tallique b et une ré duction de la porosité avec une augmentation de la vitesse de refroidissement semblaient ré sulter en une diminution de la variabilité des donné es d'UTS. IntroductionAluminium alloys with Si as a major alloying element are the most widely specified variety of alloys for automotive and aircraft applications, owing to their excellent casting characteristics, high strength to weight ratio, good mechanical properties and corrosion resistance in sand and permanent mould casting conditions. The purpose of bismuth (Bi) addition to aluminium alloys is to improve the material's machinability, promote chip breaking and help tool lubrication. However, Machovec et al. 1 reported a relatively minor effect of Bi addition on the silicon morphology of Al-Si alloys in 319 type aluminium alloy. In a previous investigation on Bi-Sr interaction on Si structure, El Haddad et al. 2 showed that with increasing addition of Bi to Sr modified 319 alloy the modification efficiency of Si diminishes. Recently, Farahany Canadian Metallurgical Quarterly 2013 ...

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 ]…”