INFLUENCE OF SOLIDIFICATION THERMAL PARAMETERS ON THE COLUMNAR TO EQUIAXED TRANSITION OF Al-Zn AND Zn-Al ALLOYS.

ALICIA ESTHER ARES; SERGIO F. GUEIJMAN; RUBENS CARAM Y .; CARLOS ENRIQUE SCHVEZOV.

San Antonio, Texas - USA

Congreso; THE 135th TMS ANNUAL MEETING EXHIBITION.; 2006

The Minerals, Metals and Materials Society (TMS).

The prediction of the columnar to equiaxed transition (CET) is of great interest for the evaluation and design of the mechanical properties of castings products. Experiments are conducted to analyze the CET during the upward unsteady state directional solidification of Al-Zn and Zn-Al alloys, under different conditions of superheat and heat transfer efficiencies at the metal/mould interface. A combined theoretical and experimental approach is developed to quantitatively determine the solidification thermal parameters: transient heat transfer coefficients, growth rates, thermal gradients and cooling rates. A numerical procedure combined with experimental results does not give support to CET criteria based either on growth rate or on temperature gradients. Rather, the analysis has indicated that a more convenient criterion should encompass both thermal parameters through the cooling rate. The effects of solidification parameters like cooling rate, growth rate, temperature gradient, melt superheat and solute concentration on the CET position are investigated.