TRANSITION BETWEEN 2 STEADY-STATES OF UNIDIRECTIONAL SOLIDIFICATION OF LANTHANUM MODIFIED AL-SI EUTECTIC

The transition between two steady states of unidirectional solidification of Al-Si eutectic modified with 0.5 wt% La has been investigated experimentally by abruptly changing the solidification rate. The addition of lanthanum results in only partial modification of the eutectic microstructure flakelike and fibrelike silicon phases being always present after solidification. The interflake spacing and the interfibre spacing are shown to have a continuous but retarded response to an abrupt change of solidification rate, the retardation of the interflake spacing being the greater. A model of the response dynamics governing the transition has been developed to interpret the results of the experiments.