Microstructure evolution during semi-solid processing of SCN-water and Sn-Pb alloys

Microstructure evolution was investigated during the solidification of succinonitrile-5at.% water transparent alloy and Sn-15 wt.%Pb alloy under mechanical stirring through in-situ observation and quenching, separately. The results showed that the evolution of primary microstructures under stirring experienced the growth of single grain particle and the successive agglomerating and coarsening of multi-particles when the particle size reached a certain value. The increase of stirring rate promoted the globular growth of solidification microstructure after it nucleated in the melt and increase the grain size. Thus, the microstructure during semi-solid processing could be refined by a controlled stirring and cooling process, which depended on the optimization among the stirring rate, cooling rate and temperature at which the stirring rate is changed.