Investigation and characterization of the nanoscale precipitation sequence and their kinetics in Al-1.0% Mg2Si-0.4 wt% Si-0.5Cu (wt%) alloy

Nonisothermal differential scanning calorimetry technique has been applied on Al-0.63 mass% Mg -0.77 mass% Si-0.5 mass% Cu alloy. Seven reaction peaks have been observed from differential scanning calorimetry (DSC). High resolution transmission electron microscopic (HRTEM) investigation has also been carried out for specimens heated with the same heating rate to the peak temperatures of the corresponding processes in the differential scanning calorimetry scans in order to characterize the developed precipitates at these temperatures. As per our results obtained from DSC and HRTEM investigations, the precipitation sequence can be written as: alpha(sss) -> Si-Mg-vacancy clusters -> GP zones -> beta ''-phase and random precipitates -> type C and/or Q'-phase -> predominant Q'-phase + a few beta(Mg2Si)-phase and Si precipitates. In addition to that, the activation energies associated with the precipitation of beta '' and Q'. were found close to the diffusion energies of Si and Mg in Al matrix. This result suggests that the diffusion of the solute atoms to form the precipitates is the appropriate mechanism of controlling both types of precipitates. (C) 2014 Elsevier B.V. All rights reserved.