Transient solidification, microstruture and properties of Al-Ni alloys / Solidificação transitoria, microestrutura e propriedades de ligas Al-Ni

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

The development of optimized microstructures during the solidification stage of processing is of fundamental importance to the mechanical properties and to the performance of finished products of metallic alloys. In this study the kinetics of solidification and its effects on macro and microstructural parameters, as well as the consequent influence on the final mechanical properties are analyzed. Hypoeutectic Al-Ni alloys are studied by upward unidirectional solidification experiments under transient heat flow conditions. Primary (?1) and secondary (?2) dendrite arm spacings are measured along the castings for all alloys analyzed and correlated with transient solidification thermal variables. A combined theoretical/ experimental approach is used to quantitatively determine such thermal variables, i.e., transient metal/mold heat transfer coefficients, tip growth rates, thermal gradients, tip cooling rates and local solidification time. The experimental data concerning the Al-Ni alloys solidification are compared to the main predictive dendritic models from the literature and the dependence of dendrite arm spacing on the alloy solute content is also analyzed. From the macrostructural point of view, it is found that the CET occurs for a critical value of cooling rate of about 0.16 K/s for hypoeutectic Al-Ni alloys.With a view to correlate mechanical properties to dendrite arm spacings, tensile testings were carried out. It is found that the ultimate tensile strength and the yield strength increase with increasing alloy solute content and with decreasing primary and secondary dendrite arm spacings. In contrast, the elongation is found to be independent of both alloy composition and dendritic arrangement. For the Al 5%Ni alloy a rapid solidification study is carried out by using laser surface remelting in order to permit microstructural and microhardness variations throughout the resulting treated and untreated zones, to be analysed

ASSUNTO(S)

solidification founding solidificação metal rapid solidification processing mechanical properties of metals metais - processos de solidificação rapida microstructure fundição microestrutura metais - propriedades mecanicas

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