Formation Mechanism of Macrosegregation

The compositional heterogeneity at the scale of industry casting is called macrosegregation. It is caused by the fact that usually solidifying crystals do not incorporate all alloying elements and thus the remaining liquid gets more and more enriched in solute. This is called (micro-)segregation. If the flow now redistributes this segregated liquid to some other location, the concentration, and with that the microstructure, will become inhomogeneous. As many different mechanisms for a relative movement between crystal and liquid exist (e.g. thermal or solutal buoyancy, sedimentation, deformation, etc.), the occurrence of macrosegregation and also the measures that can be taken to avoid their formation are numerous.

This research topic has the potential to extend our understanding of macrosegregation formation, to develop industrial relevant strategies for reducing macrosegregation, and to refine the solidification models (source codes) and to integrate them into industry 4.0 as an important part of virtual/intelligent manufacturing.

The primary aims and objectives of this research field are:

  • to use multiphase solidification models and to study macrosegregation mechanisms as caused by: - thermo-solutal convection; - crystal sedimentation; - feeding flow due to solidification shrinkage; - forced flow such as electro-magnetic stirring; - mechanical deformation of the mushy zone; - Marangoni convection.
  • to evaluate numerical models against different theoretical models or experimental benchmarks: - laboratory experiments; - Flemings theory; - industry castings.
  • to apply numerical models for different industry processes (ingots, continuous castings of steel, and direct chill casting of copper/aluminium).

Examples of recent achievements are given in Fig. 2. Further details on that research field can be found in:

  • C. M. G. Rodrigues, A. Ludwig, A. Kharicha, M. Wu: “Modelling of the twin-roll casting process: transition from casting to rolling”, Trans. of the Indian Institute of Metals71(2018) 2639-2643.
  • C. M. G. Rodrigues, A. Ludwig, M. Wu, A. Kharicha, A. Vakhrushev: “A Comprehensive Analysis of Macrosegregation Formation During Twin- Roll Casting”, Metall. Mater. Trans. B 50 (2019) 1334-50.
  • C. M. G. Rodrigues, A. Ludwig, M. Wu, A. Kharicha, A. Vakhrushev: “Two-phase viscoplastic model for the simulation of twin roll casting”, J. Mater. Process. Tech.286 (2020) 116814.
  • M. Wu, A. Ludwig, A. Kharicha: “Simulation of as-cast steel ingot - a review”, Steel Res. Int. 89 (2018) 1700037.
  • Y. Zheng, M. Wu, E. Karimi-Sibaki, A. Kharicha, A. Ludwig: “Use of a mixed columnar-equiaxed solidification model to analyses the formation of as-cast structure and macrosegregation in a Sn-10 wt% Pb benchmark experiment”, Int. J. Heat and Mass Trans. 122 (2018) 939–53.
  • M. Wu, J. Domitner, A. Ludwig: “Using a two-phase columnar solidification model to study the principle of mechanical softreduction in slab casting ”, Metall. Mater. Trans. A43 (2012), 945-963.
  • J. Domitner, M. Wu, A. Kharicha, A. Ludwig, B. Kaufmann, J. Reiter, T. Schaden: “Modeling the effect of strand surface bulging and mechanical softreduction on the macrosegregation formation in steel continuous casting”, Metall. Mater. Trans. A45 (2014), 1415-1434.
  • M. Wu, Y. Zheng, A. Kharicha, A. Ludwig: “Numerical analysis of macrosegregation in vertically solidified Pb-Sn test castings - Part I: Columnar solidification”, Comp. Mater. Sci. 124 (2016) 444-55.
  • Y. Zheng, M. Wu, A. Kharicha, A. Ludwig: “Numerical analysis of macrosegregation in vertically solidified Pb-Sn test castings – Part II: Equiaxed solidification”, Comp. Mater. Sci. 124 (2016) 456-70.
  • M. Ahmadein, M. Wu, A. Ludwig: “Analysis of macrosegregation formation and columnar-to-equiaxed transition during solidification of Al-4wt.%Cu ingot using a 5-phase model”, J. Crystal Growth 417 (2015) 65-74.

see also our Topic Related Publications