THE EFFECT OF THE SUBSTITUTION OF SILICON BY ALUMINUM ON THE PROPERTIES OF LAMELLAR GRAPHITE IRON E. Aguado, M. Ferrer, and P. Larran ˜aga A ´ rea Ingenierı ´a, I?D y Procesos Metalu ´rgicos, IK4-Azterlan, Durango, Spain D.M. Stefanescu The Ohio State University, Columbus, OH, USA The University of Alabama, Tuscaloosa, AL, USA R. Sua ´rez Veigalan Estudio, Durango, Spain Copyright Ó 2019 American Foundry Society https://doi.org/10.1007/s40962-018-00303-y Abstract In cast iron, silicon and aluminum are elements that pro- mote graphite precipitation and strengthen the alloy by solid solution. In the present work, Si has been substituted by Al leading to values that easily surpass standard properties of Fe–C–Si gray cast irons, reaching a strength of 466 MPa at moderate hardness (250 HB) for an iron with 3.08% C, 3.15% Al and 0.16% Si. Sequences of heats increasing Al content were carried out. It was found that the UTS increases with the Al content, reaching a maxi- mum at about 3% Al, after which it decreases. Graphite area measurements show a minimum at the maximum UTS, with graphite exhibiting random orientation. Carbides are avoided above 1.5% Al for very low Si content (about 0.2%) in Y2 keel blocks (25 mm thickness). Plates as thin as 2.5 mm were cast free of carbides from irons with more than 3% Al, which makes this material very desirable for thin wall castings. Additions of other elements were nec- essary, including 0.35% chromium, 0.55% manganese and 0.075% tin to obtain a pearlitic structure. Keywords: aluminum alloyed gray iron, high tensile strength gray iron, Fe–C–Al alloy Introduction Gray iron, a Fe–C–Si alloy that is one of the most common ferrous alloys used in the metal casting industry, requires silicon in its composition to avoid metastable iron carbide solidification. Because aluminum is a strong graphite pro- moter, its addition to iron is a likely substitute for silicon. Indeed, aluminum increases carbon solubility in the matrix, decreases the amount of carbon in the eutectic (C eut ) and increases the eutectic temperature up to 15% Al (Fig- ure 1). 1 Yet, because small additions of aluminum to lamellar graphite iron may promote pinholes or a greater amount of slag, iron foundries have avoided the use of aluminum in standard gray iron. However, more significant additions (e.g., 2.4% Al) have been shown to increase resistance to oxidation. 2,3 Oxidation-resistance high-alu- minum (24% Al) cast iron has also been reported. 4 A significant advancement was the development of gray iron with 2–5% Al and low silicon, which exhibited higher strength at lower hardness compared to equivalent silicon gray iron, and also good machinability. Irons with 2.8% C, 3% Al and 1% Si have been successfully cast free of car- bides in thin sections down to 3.2 mm in sand and metal molds. 5 After Defrancq et al. 6,7 reported tensile strengths of the order of 520 MPa on 30-mm rods of calcium-modified 2.5% C, 1.8% Al and 0.8% Si gray irons, the Fe–C–Al system irons were explored for applications in construction This paper is an invited submission to IJMC selected from presen- tations at the 73rd World Foundry Congress, held September 23–27, 2018, in Krakow, Poland, and has been expanded from the original presentation. International Journal of Metalcasting