The role of the primary phase on eutectic solidification of Al-Si alloys

Abstract

Thermal analyses of Al-Si alloys were carried out in order to investigate the effect of the primary phase as a site of heterogeneous nucleation for eutectic solidification.
Thermal analyses on Al-Ge and Sn-Pb alloys were also performed to support the discussions on the results of Al-Si alloys.
The results obtained were as follows.
(1) For the case of Al-Si alloys, larger undercooling was needed for nucleation of the eutectic phase when primary Si rather than primary Al was present in the melt.
(2) For the case of Al-Ge alloys larger undercooling was needed for nucleation of the eutectic phase when primary Al rather than primary Ge was present in the melt.
(3) For the case of Sn-Pb alloys, negligible undercooling was needed for nucleation of the eutectic phase when primary Sn was present in the melt. In contrast, large undercooling was obtained when primary Pb was present in the melt.
Using experimentally obtained and calculated values of interfacial energies for boundaries of liquid-primary, liquid-secondary and primary-secondary phases, the energy balances for heterogeneous nucleation were calculated and the present experimental results were found to be compatible with the calculated results.