Microstructure-based fatigue life prediction for cast A356-T6 aluminum-silicon alloys |
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Authors: | J Z Yi Y X Gao P D Lee T C Lindley |
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Affiliation: | (1) Present address: Department of Materials, Imperial College London, UK;(2) the Department of Materials Science & Engineering, University of Michigan, 48109 Ann Arbor, MI;(3) the Engineering School of Engineering and Design, Brunel University, UB8 3PH Middlesex, United Kingdom;(4) the Department of Materials, Imperial College London, SW7 2AZ London, United Kingdom |
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Abstract: | Fatigue life prediction and optimization is becoming a critical issue affecting the structural applications of cast aluminum-silicon
alloys in the aerospace and automobile industries. In this study, a range of microstructure and porosity populations in A356
alloy was created by controlling the casting conditions and by applying a subsequent hot isostatic pressing (“hipping”) treatment.
The microstructure and defects introduced during the processing were then quantitatively characterized, and their effects
on the fatigue performance were examined through both experiment and modeling. The results indicated that whenever a pore
is present at or near the surface, it initiates fatigue failure. In the absence of large pores, a microcell consisting of
α-Al dendrites and associated Si particles was found to be responsible for crack initiation. Crack initiation life was quantitatively
assessed using a local plastic strain accumulation model. Moreover, the subsequent crack growth from either a pore or a microcell
was found to follow a small-crack propagation law. Based on experimental observation and finite-element analysis, a unified
model incorporating both the initiation and small crack growth stages was developed to quantitatively predict the dependency
of fatigue life on the microstructure and porosity. Good agreement was obtained between the model and experiment. |
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