Microstructural development during transient directional solidification of a hypomonotectic Al–In alloy

Abstract

Upward directional non-steady-state solidification experiments have been performed on a hypomonotectic Al–5.5 wt%In alloy. The alloy developed cellular as-solidified microstructure for tip growth rates, V _L, higher than 0.95 mm/s. The casting regions associated with V _L < 0.95 mm/s were shown to be characterized by a microstructure formed by In droplets disseminated in the Al matrix. Tip growth rate and microstructural features, such as cell spacing and interphase spacing, have been experimentally determined. The experimental cell spacings have been compared with theoretical predictions furnished by the Hunt–Lu model. It was found that the experimental scatter lies below the minimum range of values theoretically predicted. Moreover, the experimental cell spacing evolution with V _L is characterized by a −1.1 power law. The droplets’ interphase spacing, λ, is related to the growth rate by the Jackson–Hunt relationship (λ ² V _L = constant).

Keywords:

• solidification
• monotectics
• interphase spacing
• cell spacing
• Al–In alloy

Acknowledgements

The authors acknowledge the financial support provided by FAPESP (the Scientific Research Foundation of the State of São Paulo, Brazil) and CNPq (the Brazilian Research Council) and FAEPEX-UNICAMP.