Effects of Natural Convection on the Columnar to Equiaxed Transition

CARLOS SCHVEZOV; ALICIA ARES; SERGIO GUEIJMAN; VALENTINA OKSENIUK

Beijing

Conferencia; The 16th International Conference on Crystal Growth(ICCG-16); 2010

International Union fort Crystal Growth

In a solidification process, the microstructure depends on the alloy characteristics and the temperatureevolution ahead of the solid/liquid interphase. Two of the most important micro- and macro-structuralparameters in an as cast alloy are the dendritic and grain structures respectively. An efficient method ofexamining both structural parameters is the application of directional solidification with heat extraction fromone end. In this work, Zn-1%Al and Zn-2%Al (wt%) alloys were solidified in a vertical upward (0 degrees) andinclined at 30 ° and 45 ° to the vertical (gravity) direction. For these solidification conditions the position of thetransition from columnar to equiaxed structure (CET)was determined, as well as the significant thermalparameters..The main results obtained in samples of 120 mm-length and (22 ± 1) mm-diameter are: a) the transition occursin a zone of about 10 mm or greater, where coexist columnar and equiaxed grains, b) in the three directions,where CET occurs the temperature gradient reaches critical values, c) the angle of inclination of the columnargrains with the longitudinal axis of the sample coincides approximately with the angle of the furnace, d) thethermal parameters (cooling rates, Liquidus and Solidus interphase velocities and temperature gradients) at theinstant of the CET were measured and compared with previous results of samples solidified vertically upward