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Materials 2016, 9(3), 126;

The Effect of Bi-Sr and Ca-Sr Interactions on the Microstructure and Tensile Properties of Al-Si-Based Alloys

Département des Sciences appliquées, Université du Québec à Chicoutimi, Chicoutimi, QC G7H 2B1, Canada
General Motors Powertrain Group, Materials Technology, Pontiac, MI 48430, USA
Corporativo Nemak, S.A. de C.V., P.O. Box 100, Garza Garcia, N.L. 66221, Mexico
Author to whom correspondence should be addressed.
Academic Editor: Daolun Chen
Received: 21 December 2015 / Revised: 13 February 2016 / Accepted: 18 February 2016 / Published: 25 February 2016
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The effect of bismuth and calcium additions on the microstructural characteristics and the tensile properties of the modified and grain-refined Al-Si based B319 alloys were studied in this paper. Based on the results obtained, it has been concluded that Bi reacts with both Sr and Mg, leading to severe demodification of the eutectic Si at Bi levels of 0.15%–0.6% Bi. Bismuth causes a decrease of the yield and tensile strengths for the as-cast and artificially aged conditions and an increase of yield strength in the solution heat-treated condition. The elongation increases with the Bi in the solution heat-treated condition. Based on this, Bi is found to be an efficient solid-solution strengthening element for these alloys. Thus, solution heat treatment, rather than the artificial aging, may be recommended for alloys containing about 1.0% Bi. Calcium has no significant demodification effect on the Sr-modified Si particles at 100–400 ppm Ca, and has a modifying effect at ~600 ppm Ca. The elongation increases with the Ca level at all conditions (as-cast, solution heat-treated, and artificially aged). A slight increase of the tensile strength in the heat-treated conditions was also observed. The lowest tensile properties either in the as-cast or the heat-treated conditions correspond to the most demodified-Si condition obtained at 408 ppm Ca. Calcium is, therefore, not as detrimental to the tensile properties as Bi. View Full-Text
Keywords: Al-Si-(Cu) alloys; Ca; Bi; Sr; P; modification; demodification Al-Si-(Cu) alloys; Ca; Bi; Sr; P; modification; demodification

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Samuel, A.M.; Doty, H.W.; Gallardo, S.V.; Samuel, F.H. The Effect of Bi-Sr and Ca-Sr Interactions on the Microstructure and Tensile Properties of Al-Si-Based Alloys. Materials 2016, 9, 126.

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