Characterization and kinetic modeling of secondary phases in squeeze cast Al alloy A380 by DSC thermal analysis

Abstract

Thermal analyses on squeeze cast aluminum alloy A380 (SC A380) solidified under 90 MPa were carried out to study the microstructure development of the alloy, in which a differential scanning calorimeter (DSC) was employed. During the DSC runs, heating and cooling rates of 1, 3, 10, and 20 °C•min-1 were applied to investigate the heating and cooling effects on dissolution of secondary eutectic phases and microstructure evolution. Various reactions corresponding to troughs and peaks of the DSC curves were identified as corresponding to phase transformations taking place during dissolution or precipitation suggested by the principles of thermodynamics and kinetics. The comparison of the identified characteristic temperatures in the measured heating and cooling curves are generally in good agreement with the computed equilibrium temperatures. The microstructure analyses by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) indicate that the distribution and morphology of secondary phases present in the microstructure of the annealed sample are similar to the as-cast A380, i.e., strip β(Si), buck bone like or dot distributed θ(Al2Cu), β(Al5FeSi) and Al15(FeMn)3Si2. Two kinetic methods are employed to calculate the activation energies of the three common troughs and three common peaks in DSC curves of SC A380. The activation energies of the identified reaction θCuAl2 = α(Al)+β(Si) is 188.7 and 187.1 kJ∙mol-1 when the activation energies of reaction α(Al)+β(Si)→θCuAl2 is -122.7 and -121.8 kJ∙mol-1, by the Kissinger and Starink methods, respectively.

Keywords

• thermal analysis; DSC; secondary phase; activation energy; SC A380