CONICET | Buscador de Institutos y Recursos Humanos

Polycrystalline structures formation in fabrication process is depending of characteristics of alloy solidification and the temperature distribution in the solidification front. One of the most important phenomena present in the solidification process is the polycrystalline dendritic growth. In the present research the Zn-16wt %Al alloys were solidified directionally upwards This alloys combine high strength and hardness, good machinability with good bearing properties and wear resistance often superior to standard bronze alloys. To study the correlation between the polycrystalline dendritic structure and the thermal parameters during solidification, the alloys were solidified under known solidification velocity and direction, and temperature profiles with a set of six thermocouples in the samples, which permit to determine the time dependent profiles during growth. From these profiles and the location of the thermocouples, it was possible to calculate the growth velocity and the temperature gradients along the sample. After solidification, the sample was cut along the axis, or solidification direction. One of the halves was cut at the positions close to the thermocouple positions by observation in the cross section transversal to the growth direction. The samples were mounted, polished and etched for observation of the structure. Different thermal analysis of the alloys was performed to determine the beginning and end of solidification. The primary and secondary arm dendritic spacing was measured and correlated with solidification velocity, local solidification time, temperature gradient and position in the sample. Directional growth of zinc-based polycrystalline alloys was performed and the temperatures during the whole process measured in the liquid and solid phases. The secondary spacing increases with an increase of the local solidification time. The primary and secondary spacings reach peak values in the columnar to equiaxed region.

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