PARÂMETROS TÉRMICOS, MACROESTRUTURA E MICROESTRUTURA NA SOLIDIFICAÇÃO DIRECIONAL DA LIGA Al-20%Sn
THERMAL PARAMETERS, MACROSTRUCTURE AND MICROSTRUCTURE DURING DIRECTIONAL SOLIDIFICATION OF AN Al-20wt%Sn ALLOY
Cruz, Kleber Agustin S. da; Cheung, Noé; Garcia, Amauri
http://dx.doi.org/10.4322/tmm.00404004
Tecnol. Metal. Mater., vol.4, n4, p.21-26, 2013
Resumo
As ligas Al-Sn são muito empregadas em aplicações tribológicas e seus componentes têm a característica de serem praticamente imiscíveis, sendo que o tipo de arranjo microestrutural decorrente induz boa resistência ao desgaste. Neste trabalho, foram realizadas análises térmicas e microestruturais ao longo de um lingote de liga Al-20%Sn, obtido por solidificação unidirecional transitória na direção vertical e sentido ascendente. O mapeamento térmico permitiu a obtenção do coeficiente global de transferência de calor metal/molde (hg), com a utilização do método do confronto de perfis térmicos experimentais e simulados numericamente, e da evolução de variáveis térmicas (velocidade de deslocamento da isoterma liquidus e taxa de resfriamento) durante o processo. A caracterização da microestrutura dendrítica foi feita por meio de medidas dos espaçamentos secundários (λ2), que foram devidamente correlacionados com variáveis térmicas de solidificação. A liga Al-20%Sn mostrou um comportamento semelhante ao de outras ligas de alumínio, ou seja, a rede dendrítica tornou-se mais grosseira com a redução da taxa de resfriamento, indicando que a condição de imiscibilidade entre o alumínio e o estanho não interferiu na forma da relação entre espaçamento dendrítico e taxa de resfriamento. É determinada uma lei experimental de crescimento dendrítico.
Palavras-chave
Liga aluminio-estanho, Estrutura dendrítica, Parâmetros térmicos, Solidificação
Abstract
Al-Sn alloys are widely used in tribological applications. Aluminium and tin form immiscible alloys and the type of the microstructural arrangement causes a good wear resistance. In this study, thermal and microstructural analysis were carried out along an Al-20wt%Sn alloy ingot produced by vertical upward directional transient solidification. The experimental thermal readings were fitted to numerical predictions in order to determine the global heat transfer coefficient (hg) and were also used to calculate the evolution of thermal variables (tip growth rate and cooling rate) during solidification. The growth rate and the cooling rate play a key role in the microstructural formation. The dendritic microstructure has been characterized by secondary dendritic arm spacings (λ2) which were experimentally determined and correlated to solidification thermal variables. The behavior presented by the Al-20wt%Sn alloy during solidification was similar to that of other aluminum alloys, i.e., the dendritic network became coarser with decreasing cooling rates, indicating that the immiscibility between aluminum and tin has not a significant effect on the relationship between the secondary dendritic arm spacing and cooling rate. An experimental dendritic growth law has been determined.
Keywords
Alloy Al-Sn, Dendritic structure, Thermal parameters. Solidification
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