Modification of near-eutectic Al-Si alloys with rare earth element samarium
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i Hu Department of Materials Processing Engineering, School of Mechanical Electrical Engineering, Nanchang University, Nanchang 330031, China; and Jiangxi Key Laboratory for Advanced Copper and Tungsten Materials, Jiangxi Academy of Sciences, Nanchang 330031, China (Received 9 January 2014; accepted 13 May 2014)
The modification of near-eutectic Al–Si alloy with samarium additions (0–0.9 wt.% content) has been studied. The thermal analysis results indicated that the addition of Sm in Al–12Si alloy caused a depression of eutectic temperature (ΔTE). And it was found that Sm was capable of breaking down the primary a-A1 phases, giving rise to an increment in the number of dendrites. Simultaneous primary Si refinement and eutectic modification were achieved by Sm addition. When 0.6 wt.% Sm was added to the alloy, the silicon in Al–12Si alloy was best refined and showed a fully modified, fine fibrous eutectic structure; the primary a-Al phase appears as a slightly dual dendritic-cellular nature and a pine-tree structure. Moreover, the mechanical properties were investigated by the tensile test. A good combination of ultimate tensile strength (217 MPa) and elongation (1.3%) was obtained when the addition of Sm was up to 0.6 wt.%.
I. INTRODUCTION
Silicon is probably one of the least expensive alloying additions commonly made to aluminum, which improves castability, increases strength to weight ratio, enhances corrosion resistance, decreases the coefficient of thermal expansion, and imparts wear resistance to aluminum.1,2 Due to the increasing requirement to reduce vehicle weight and to improve fuel economy, aluminum–silicon (Al–Si) alloy castings have been found the most widespread use in automobile. Eutectic and near-eutectic Al–Si casting alloys attract more attention due to its excellent castability and lower cost of raw materials compared with A356 alloys.3–5 Commercial eutectic and near-eutectic Al–Si alloys exhibit a hypereutectic microstructure normally consisting of a-Al dendrites, eutectic Si of an acicular and/or laminar morphology, primary silicon phase of a polygonal morphology.6 Large cuboid-shaped primary silicon and acicular eutectic silicon particles are known to deteriorate mechanical and friction performance of Al–Si alloys. Modification of Si phases in Al–Si alloys is carried out extensively in industry to improve mechanical properties. Traditionally, P, Na, Sr, and B are added as modifiers to Al–Si alloys,7–9 and the eutectic microstructure is a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.113 1270
J. Mater. Res., Vol. 29, No. 11, Jun 14, 2014
http://journals.cambridge.org
Downloaded: 08 Oct 2015
converted from a coarse flake to a fine fibrous morphology and large cuboid-shaped primary silicon particles were refined simultaneously. Nogita et al.10 investigated the eutectic silicon modification efficiency of fourteen kinds of rare earth elements in Al–10Si alloy. It suggested that the structural transition was limited to a refinement of the coarse plate-like silicon str
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