CONICET | Buscador de Institutos y Recursos Humanos

Components manufactured from cast aluminum alloys offer the advantages of lower cost and higher strength-to-weight ratios compared to ferrous alloys and Zn-Al (ZA) alloys combine high strength and hardness, good machinability with good bearing properties. The most common structure in solidification of metallic alloys is the dendrite, which can be either columnar, equiaxed or transitional from columnar to equiaxed (CET microstructure). In the present research we investigate correlations between thermal parameters, grain size, dendritic spacing and microhardness in directional solidified samples of Al-Zn and Zn-Al alloys which present different types of structures: columnar, equiaxed and the CET. We analyze the correlation between cooling rate and dendritic spacing in columnar and equiaxed grains. Also correlations between grain size and dendritic arm spacing and the variations in microhardness were investigated as a function of both microstructure and load applied in the directionally solidified alloys. We concluded: a) the width of the columnar grains decreases with the cooling rate, b) the columnar length can be estimated within the transition region from the position of the fronts and a parameter C that was determined for each alloy, c) the density of equiaxed grains is linearly related to the temperature gradient, d) the secondary arm spacing increases with an increase of the local solidification time, e) the microhardness values decrease when the load increase and reach almost constant values at higher loads and f) bulk alloys have similar microhardness values than those in the equiaxed zone of the directionally solidified samples.

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