Hi Mr. Betz,
When I was in graduate school I did a fair amount of modeling of the semi-continuous direct chill (DC) casting process for aluminum alloys which also commonly has a compositionally enriched area near the surface. There are several works that discuss this phenomena in detail, below are a few of them:
Vreeman, C. J., Schloz, J. D., and Krane, M. J. M. (September 11, 2002). "Direct Chill Casting of Aluminum Alloys: Modeling and Experiments on Industrial Scale Ingots ." ASME.
J. Heat Transfer. October 2002; 124(5): 947–953.
https://doi.org/10.1115/1.1482089
Založnik, M., Kumar, A., Combeau, H., Bedel, M., Jarry, P., Waz, E., 2011. Influence of Transport Mechanisms on Macrosegregation Formation in Direct Chill Cast Industrial Scale Aluminum Alloy Ingots. Adv. Eng. Mater. 13, 570–580. https://doi.org/10.1002/adem.201000341
Eskin, Dmitry G., and Laurens Katgerman. "Macrosegregation Mechanisms in Direct-Chill Casting of Aluminium Alloys." Materials Science Forum, vol. 630, Trans Tech Publications, Ltd., Oct. 2009, pp. 193–199. Crossref, doi:10.4028/www.scientific.net/msf.630.193.
Kyle Fezi, Alex Plotkowski & Matthew John M. Krane (2016) Macrosegregation modeling during direct-chill casting of aluminum alloy 7050, Numerical Heat Transfer, Part A: Applications, 70:9, 939-963, DOI: 10.1080/10407782.2016.1214508
The mechanism in DC casting is due to shrinkage driven flow deep in the mushy zone which redistributes the interdendritic liquid perpendicular to the solidification front. This flow causes the surface to become locally enriched.
Regards,
Kyle Fezi
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Kyle Fezi
Fort Wayne Metals
Columbia City IN
1.260.438.9149
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Original Message:
Sent: 11-30-2020 11:36
From: David Betz
Subject: Segregation during solidification
Greetings!
I am looking for help understanding some segregation phenomena, specifically in aluminum alloys, although I can see the topic being relevant to other alloy systems. While it would be nice to have the answers through a discussion here, I would also be interested in references to articles / papers that I could acquire and review.
I was recently reading an article on the influence of mold design (for OES cast buttons) on the results from OES testing of said buttons (Fortier and Trembley 1984). In it, they state that "For elements forming eutectics with aluminium (like Fe, Si, Mg, etc.), there is usually an enrichment in the zones which are cooled first, that is to say, toward the walls of the sample. For peritectic elements (like Ti), the phenomena is inverse, the enrichment is found toward the zone which is cooled last."
I am looking to understand this better. I remember from my metallurgy courses, when a hypoeutectic material is solidified (non-equilibrium), the first material to solidify is more "pure" while the remaining liquid becomes more highly alloyed. This (to my mind) contradicts the phenomenon that eutectic elements solidify first. Which means I need to expand my knowledge, because it does happen.
Thank you, in advance, for your help!
David Betz
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David Betz
Sr. Laboratory Engineer
Hydro Aluminum Metals, USA
dbetzasm@gmail.com
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