Evaluation of the Growth Kinetics of θ′ and θ-Al2Cu Precipitates in a Binary Al-3.5 Wt Pct Cu Alloy

Abstract

Heat treatment for precipitation hardening is known to have a significant effect on the nano/microstructure of cast aluminum alloys, and thereby affecting its properties. In this study, precipitation kinetics after solutionizing and water quenching have been characterized by differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and microhardness evaluations under different aging conditions. The Kissinger methodology was applied along with the Lee–Kim–Starink–Zahra kinetic equation to determine the kinetic parameters from the DSC runs at constant heating rates, assuming that the precipitates have an ellipsoidal shape. The TEM results showed evidence of semi-coherent θ′ precipitation in accordance with the microhardness evolution during isothermal aging at 190 °C and the kinetic analysis from the DSC data. The TEM bright field images of the specimens aged at two different times were used to record the size and number density of the precipitates. The activation energies for the precipitation kinetics of θ and θ′ were 330 and 114 kJ/mol, respectively. Finally, the values for the interfacial mobility were determined using the kinetic parameters derived from the DSC results and the TEM observations.