Effects of Iron-Rich Intermetallics and Grain Structure on Semisolid Tensile Properties of Al-Cu 206 Cast Alloys near So
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THE semisolid tensile behavior of solidified aluminum alloys has recently received considerable attention.[1–5] Due to the thermal gradients and solidification shrinkage during the casting process, the semisolid microstructure is frequently subjected to tensile stresses, which can lead to casting defects such as hot tearing and porosity.[6–8] The response of the solidified microstructure to the applied stress depends on the deformation behavior, tensile properties, and liquid flow within the semisolid structure (mush structure).[9–11] To investigate the mechanical properties of aluminum alloys in the semisolid state, three major mechanical tests in shear,[7,12,13] compression,[7,14,15] and tension[4,7,11,16–19] have been developed. It is widely accepted that the semisolid tensile test induces a similar stress–strain condition to that during solidification of the aluminum alloy.[7,17] Therefore, the semisolid tensile test can provide accurate quantitative results for the tensile properties of the semisolid alloy.[2,3,17,20–26] Moreover, the microstructural observations of the mechanically tested samples may show that the microstructural evolution is similar to those during solidification.[1,27–30] These capabilities provide a deeper understanding of the
AMIR BOLOURI, Postdoctoral Fellow, KUN LIU, Research Professor, and X.-GRANT CHEN, Professor, are with the Department of Applied Science, University of Quebec at Chicoutimi, Saguenay, QC G7H 2B1, Canada. Contact e-mail: xgrant_chen@ uqac.ca Manuscript submitted April 27, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
deformation mechanisms of the mush structure under the stresses from the solidification process.[8] The tensile behavior and deformation mechanisms of the mush structure as a function of the solid fraction have been the subject of a number of studies.[20–27] Studies to determine the semisolid tensile properties of different aluminum alloys, including AA5182,[2,4] AA3014 and AA6111,[3,4] 7xxx,[5] and AA6061,[17] have been conducted. The results from those prior studies indicate that all semisolid materials lost their ductility at a solid fraction, fs, of ~0.95 to 0.98, and their strength at a fs of ~0.90 to 0.95.[3] However, there is limited information on the effect of constitutive phases such as Fe-rich intermetallics on the semisolid tensile properties of aluminum alloys during the last stage of solidification. The morphology, size, and distribution of these intermetallics are important for the formation of casting defects such as hot tearing.[28,31] Furthermore, a careful examination of the effect of grain structure on the tensile properties of the mush is rarely found in the literature. Al-Cu cast 206 alloys possess great potential to achieve excellent mechanical properties comparable to those of forged and wrought aluminum alloys.[32,33] In addition, they have a promising high-temperature tensile strength.[34] However, 206 cast alloys are susceptible to hot tearing during the casting process.[35,36] Iron is one of the most common impurities in alumin
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