Abstract
The solidification experiment of Al-9.5 wt.% Zn alloy was conducted under both normal gravity and microgravity conditions by using a 50-m-high drop tube. The solidification microstructure was observed by using optical microscope. The amounts, morphologies together with sizes of the grains in the remelting regions on longitudinal sections of the samples were statistically analyzed with the image analysis software. Moreover, the axial and radial composition distributions were studied by applying SEM–EDX. The results show that the remelted solidification structure morphologies of the samples can be roughly divided into three categories, the small equiaxed grains formed by initial chilling, the elongated columnar crystals and the coarse equiaxed grains at the end, but the amount, size and morphology of the grains are different in the samples solidified under the two gravity conditions. The number of grains obtained in μg sample is larger, and the grain size distribution concentrates in small size intervals. Some pores were observed in the small equiaxed grain regions formed at the early stage of solidification in both samples, and several pores were also observed in the coarse equiaxed grain region formed at the later stage of solidification merely in μg sample. In addition, the distributions of solute element in radial and axial direction are more uniform in μg sample, while solute content in 1g sample fluctuates greatly and tends to converge towards the lower part of the sample. The above results suggest that under normal gravity condition, buoyancy convection could lead to the lower temperature gradient and supercooling, which reduced the nucleation rate. Meanwhile, buoyancy could let nuclei float up and melt rich of Zn flow down, and thus promoted grain growth and downwards segregation of Zn solute as well. Besides, buoyancy could drive bubbles to float up and facilitated them to escape from the melt.
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This research was supported by the China manned space engineering (TGJZ800-2-RW024).
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This article belongs to the Topical Collection: Research Pioneer and Leader of Microgravity Science in China: Dedicated to the 85th Birthday of Academician Wen-Rui Hu
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Kong, Y., Luo, X., Li, Y. et al. Role of Gravity in Grain and Bubble Morphology Evolution During Solidification of Al-9.5 Wt.% Zn Alloy. Microgravity Sci. Technol. 34, 48 (2022). https://doi.org/10.1007/s12217-022-09951-6
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DOI: https://doi.org/10.1007/s12217-022-09951-6