Caracterização da microestrutura dendritica na solidificação vertical descendente de ligas AL-CU / Characterization of dendritic array during downward transient directionally solidified AL-CU alloys

AUTOR(ES)

Daniel Monteiro Rosa

DATA DE PUBLICAÇÃO

2004

RESUMO

The dendritic spacings are important microstructural parameters, involved in solidification processes. They can affect not only microsegregation profiles but also the formation of secondary phases within interdendritic regions, which influences mechanical properties of cast structures. A small number of studies have been carried out in order to analyze the effects of melt convection within the interdendritic region or to verify the influence of growth direction on dendritic arm spacings. In this work, an experimental set-up of downward solidification with a stainless steel mold, having an internal diameter of 56mm, height 150mm and wall thickness of 10mm, was used. The upper part of the split mold was closed with a water-cooling chamber made of stainless steel, with a wall thickness of 3 mm. Besides, a combined theoretical and experimental approach is developed to quantitatively determine solidification thermal variables such as: transient metallmold heat transfer coefficient, tip growth rate, thermal gradient, tip cooling rate and local solidification time during downward transient solidification of hypoeutectic AI-Cu alloys solidified downwards (Al-3wt%Cu, Al-5wt%Cu and Al-8wt%Cu). These solidification thermal variables are correlated with dendritic spacings (primary and secondary spacings), which have been measured along cross and longitudinal sections of ingots solidified under downward transient heat flow conditions. Predictive theoretical models for dendritic spacings have been compared with experimental observations. A comparison between upward and downward unsteady-state results for dendritic spacings has also been conducted

ASSUNTO(S)

solidification microestrutura calor - convecção ligas de aluminio-cobre convection of heat solidificação microstructure aluminium-copper alloys

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