Abstract
As-cast aluminum-7 wt.% ailicon alloy sample rods were re-melted and directionally solidified on Earth which resulted in uniform dendritically aligned arrays. These arrays were then partially back-melted through an imposed, and constant, temperature gradient in the microgravity environment aboard the International Space Station. The mushy zones that developed in the seed crystals were held for different periods prior to initiating directional solidification. Upon return, examination of the initial mushy-zone regions exhibited significant macrosegregation in terms of a solute-depleted zone that increased as a function of the holding time. The silicon (solute) content in these regions was measured on prepared longitudinal sections by electron microprobe analysis as well as by determining the fraction eutectic on several transverse sections. The silicon content was found to increase up the temperature gradient resulting in significant silicon concentration immediately ahead of the mushy-zone tips. The measured macrosegregation agrees well with calculations from a mathematical model developed to simulate the re-melting and holding process. The results, due to processing in a microgravity environment where buoyancy and thermosolutal convection are minimized, serve as benchmark solidification data.
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Notes
In this article, “wt.%” is dropped; so Al- 7 wt.% Si is simply designated as Al-7Si.
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Acknowledgements
This work was supported by National Aeronautics and Space Administration (NASA) Grant NNX08AN49G and NNX14AJ73G. The Al-7% Si alloys for this research were kindly provided by Dr. Men G. Chu at ALCOA Technical Center. M. Lauer would like to acknowledge support from the Sandia National Laboratories Campus Executive Fellowship program.
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Lauer, M., Ghods, M., Angart, S.G. et al. Macrosegregation During Re-melting and Holding of Directionally Solidified Al-7 wt.% Si Alloy in Microgravity. JOM 69, 1289–1297 (2017). https://doi.org/10.1007/s11837-017-2380-0
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DOI: https://doi.org/10.1007/s11837-017-2380-0