Observations of the Columnar-to-Equiaxed Transition in Directionally Solidified Zinc-Aluminum Alloys and Composites

A. E. ARES; C. E. SCHVEZOV

Honolulu-Hawaii, USA.

Conferencia; THE SEVENTEENTH ANNUAL INTERNATIONAL CONFERENCE ON COMPOSITES/NANO ENGINEERING (ICCE - 17); 2009

International Community for Composites Engineering and College of Engineering, University of New Orleans.

In general, equiaxed structures have bigger resistance, longer durability to fatigue, second phases more finely dispersed, better impact properties and workability. On the other hand, columnar structures commonly obtained in the production of turbine blades, have bigger resistance to traction and compression, larger resistance to flexion and larger resistance to torsion. The interaction between the parameters involved in the columnar to equiaxed transition (CET) has gained considerable attention over the last three decades in order to understand the structure of ingot castings and to optimize the industrial practice.There are no studies of the CET in composites directionally solidified in the literature. The results presented in this paper focus on the CET studies in Zn-Al alloy systems with different compositions and with reinforcing particles of silicon carbide and alumina. The effects of several solidification parameters on the transition are determined and discussed. Such parameters include the position of the solidification fronts given by the liquidus and solidus temperatures, cooling rate of the liquid, temperature gradient, superheat, heat flow and recalescence.After solidification the structure was analyzed. The analyses were done performing quantitative metallography and composition analysis of the different alloying elements along solidified samples utilizing SEM (Scanning Electron Microscopy) and EDXA (Energy Dispersive X-Ray Microanalysis).