THE INFLUENCE OF SOLIDIFICATION DIRECTION ON THE CET IN ZN-BASE ALLOYS

ALICIA ESTHER ARES; MARÍA VALENTINA OKSENIUK; CARLOS ENRIQUE SCHVEZOV; SERGIO FABIAN GUEIJMAN

Madrid

Congreso; XXII IUCr CONGRESS; 2011

IUCr

Zinc gravity casting alloys can be used for general industrialapplications where strength, hardness, wear resistance or good pressuretightness is required. Zinc alloys are often used to replace cast ironbecause of their similar properties and higher machinability ratings.The composition of hypoeutectic alloys is close to 4%wtAl andtheir aluminum content is greater than that of eutectic alloys (5%wtAl).All zinc casting alloys have dendritic/eutectic microstructures.However, hypoeutectic alloys solidify with zinc-rich dendrites, whereashypereutectic alloys solidify with aluminum-rich dendrites.In a solidification process, the microstructure depends on the alloycharacteristics and is mainly a function of the temperature evolutionahead the solid/liquid interphase [1-3].Among the several phenomena occurring during solidification, likesolute segregation or morphology stability, one of the most importantones is dendritic growth. The most important dendrite parameters arethe primary, secondary and tertiary arm spacings due to their influenceon mechanical properties.An efficient method to examine the evolution of the dendrite armsis related to the application of steady-state directional solidificationwith an imposed growth rate, V, and a thermal gradient, G, at the solid/liquid interphase.In this work, Zn-Al (wt%) alloys were solidified underunidirectional solidification in a device cooled with water, in a verticalupward direction (0º), inclined at 30° and 45° to the vertical and in ahorizontal upward direction (90º to the vertical). We determined theposition of the transition from columnar to equiaxed structure (CET)through macro and micro-analysis, and significant thermal parametersby recording temperature-time data. The results show that the directionof dendrite growth is about that of the heat extraction and that the angleof inclination of the columnar grains with the longitudinal axis of thealloy sample coincides approximately with the angle of inclination ofthe furnace.The relevance of the problem under study is justified on the basisthat the solidification variables, including natural convection, affect thestructures of the solid and the formation of defects. The solidificationvariables are also important for modeling prediction of the structureand property of a given cast piece [3-11]. The results also allow abetter understanding of the conditions and mechanisms operating in asolidification with different directions.