Combined effect of bismuth content and cooling rate on microstructure and mechanical properties of Al–8?5Si–0?4Mg–0?3Fe alloy S. Farahany* 1 , A. Ourdjini 1 , M. H. Idris 1 , A. V. Takaloo 2 and L. T. Thai 1 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 4uCs 21 ) on the microstructure, tensile characteristics, quality index and two- parameter 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 4uCs 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 e ´tude examine l’effet combine ´ de la teneur en Bi (0?1, 0?2, 0?4 et 0?5% en poids) et de la vitesse de refroidissement (de 0?7a `4uCs 21 ) sur la microstructure, les caracte ´ ristiques de tension, l’index de qualite ´ et deux modules de Weibull d’un alliage d’Al–8?5Si–0?4Mg–0?3Fe. Les re ´ 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’e ´paisseur de l’interme ´ tallique Al 5 FeSi-b diminuait avec une augmentation de la vitesse de refroidissement, mais on n’a pas observe ´ d’effet important avec l’addition de Bi. Les trace ´s du contour des proprie ´te ´s me ´caniques sugge `rent que l’effet de la vitesse de refroidissement sur les proprie ´te ´ s me ´ caniques e ´tait plus important que celui des additions de Bi. On a obtenu le module de Weibull le plus e ´ leve ´ pour l’alliage de base et pour l’alliage contenant du Bi a ` la vitesse de refroidissement de 4uCs 21 . La diminution de l’e ´ paisseur de la phase interme ´ tallique b et une re ´duction de la porosite ´ avec une augmentation de la vitesse de refroidissement semblaient re ´sulter en une diminution de la variabilite ´ des donne ´es d’UTS. Keywords: Bismuth, Cooling rate, Aluminium alloys, Solidification, Weibull Introduction Aluminium 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 resis- tance 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 1 Department of Materials Engineering, Faculty of Mechanical Engineering Universiti Teknologi Malaysia, 81310, Johor Bahru, Malaysia 2 Research Institute of Advanced Materials, Department of Materials Science and Engineering, Seoul National University, Seoul 151-742, Korea *Corresponding author, email saeedfarahany@gmail.com 208 ß 2013 Canadian Institute of Mining, Metallurgy and Petroleum Published by Maney on behalf of the Institute Received 14 March 2012; accepted 17 September 2012 DOI 10.1179/1879139512Y.0000000045 Canadian Metallurgical Quarterly 2013 VOL 52 NO 2