Modeling of solute-driven resolidification in Al-Cu alloys inspired by false-bottom ice formation in seawater

Kurzfassung

The formation of false-bottom ice beneath melting sea ice provides a natural example of phase evolution governed by coupled heat and solute transport [1]. Inspired by this phenomenon, we investigate Al–Cu alloys as a controlled model system for studying partial melting, solute redistribution and resolidification. The analogy is based on phase equilibrium, concentration gradients and evolving solid–liquid regions, while differences in material properties and boundary conditions are retained.

We combine established analytical moving-boundary descriptions with experimental observations. In the false-bottom model, a quasi-equilibrium mushy layer is bounded by two moving interfaces, whose evolution follows from interfacial heat and solute balances [1]. The model provides predictions of interface motion, layer thickness, temperature and salinity distributions, solid fraction and heat exchange. We discuss the relevance of these results to metallic model experiments and the adaptations required for their quantitative comparison. Phase-field modeling from earlier Al–Cu studies provides a complementary description of solute redistribution [2].

Published experiments on compositionally graded Al–Cu samples subjected to isothermal holding established the experimental starting point [2]. The current Jena–DLR work extends these investigations to in-situ X-ray radiography during partial melting and holding in a temperature gradient, complemented by microscopy and elemental analysis after cooling. The observations reveal moving interfaces and evolving structural features, while the resulting samples provide concentration gradients for subsequent investigations.

Together, these approaches provide a basis for quantitative testing of moving-boundary models and guide further experiments on samples with characterized concentration profiles. The work connects a natural ice-growth phenomenon with controlled studies of phase transformations in metallic alloys.

References:

[1] D. V. Alexandrov and I. G. Nizovtseva, “To the theory of underwater ice evolution, or nonlinear dynamics of ‘false bottoms’,” International Journal of Heat and Mass Transfer 51 (2008), 5204–5208. DOI: 10.1016/j.ijheatmasstransfer.2007.11.061. [2] I. Nizovtseva, V. Ankudinov, E. Rahner and S. Lippmann, “Climate related phase transitions with moving boundaries by virtue of mushy zone investigation in Al–Cu: Experiment and phase-field modeling,” Mathematical Methods in the Applied Sciences 47 (2024), 6853–6867. DOI: 10.1002/mma.9901.