Hot-Tearing Assessment of Multicomponent Nongrain-Refined Al-Cu Alloys for Permanent Mold Castings Based on Load Measure
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SABAU, AMIT SHYAM, and J. ALLEN HAYNES are with the Oak Ridge National Laboratory, Oak Ridge, TN 37831. Contact e-mail: [email protected] SEYED MIRMIRAN and CHRISTOPHER GLASPIE are with the Fiat Chrysler Automobiles North America, LLC., Auburn Hills, MI 48326. SHIMIN LI and DIRAN APELIAN are with the Worcester Polytechnic Institute, Worcester, MA 01609. ANDRES F. RODRIGUEZ is with the Nemak Monterrey, Garcia, 66000, Mexico. This submission was sponsored by a contractor of the United States Government under contract DE-AC05-00OR22725 with the United States Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan). Manuscript submitted June 21, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
INTRODUCTION
A primary challenge for the high-volume production of automotive cast metal parts is the reduction of casting defects. Hot tearing is one of the most detrimental casting solidification defects.[1] The shapes of ‘‘hot-tear’’ defects are irregular, corresponding to those of the interdendritic regions. The appearance of hot-tear defects depends on both the local state of stress and interdendritic feeding. Concerning mechanical properties, the material in the ‘‘mushy zone’’ can be regarded as a porous metallic material saturated with its liquid phase.[2] Due to the thermal contraction of the solid phase during alloy solidification, stress can build up after the dendritic network is coherent, i.e., the dendrites are interconnected. In addition, stresses build up in casting regions due to the geometric constraint of the mold. The interdendritic liquid flow takes place to compensate for solidification shrinkage, thermal contraction of the solid phase during its cooling, and local deformation of solid phase. When the interdendritic liquid flow can feed these local deformation regions, in
which dendrite arms are pulled apart over a significant distance, the space between displaced dendrite arms is filled, and the hot tears are ‘‘healed.’’ This ‘‘healing’’ of hot tears is expected to occur as long as interdendritic flow of liquid metal is maintained. As solidification proceeds, the solid fraction increases, the area open for interdendritic fluid flow decreases, and liquid feeding of solidification shrinkage becomes more difficult. Thus, at high-volume fraction of solid, an opening of the dendritic network caused by tensile deformation is likely to remain unfilled, allowing cracks to nucleate and grow, and causing a ‘‘hot tear’’ defect.[3] Early studies on hot tearing, such as those by Lees[4] and Rosenberg et al.,[5] were concerned with determini
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