Abstract: Solidification is an important branch of material science. By model calculation and in-situ observation in this work, distinct from traditional solidification of continuous solid growth, the evolution of discrete solidification was investigated, and a new principle for discrete solidification is established based on segregation evolution in a semi-solid matrix. The solidification evolution of Al-2 wt.%Cu alloy was investigated by model calculation under different initial undercooling and cooling rates, under superimposed multi-scale temperature fluctuations, and under variable temperature fluctuations. The initiation and propagation of segregation fluctuations in semi-solid matrix were verified within a traditional dendritic arm. The alternate solid elements evolved from semi-solid matrix act as periodic dams inhibiting serious segregation. Based on the new solidification principle, a multi-scale dendritic pattern was reproduced in a two-dimensional calculation. The new solidification principle reveals the essence of multi-scale microstructures as multi-scale segregation patterns and highlights the feasibility of controlling multi-scale microstructures and segregations.

Key words: Solidification principle, Dendrite, Segregation, Semi-solid matrix