Kinetics of Precipitation Hardening Phases in Recycled 2017A Aluminum Alloy

Kinetic parameters that describe phase transformation and precipitation rates include the activation energy. In Al based alloys, volume fractions of precipitates, the melting temperature of specific phases and the activation energy of reactions can, in most cases, be determined by the differential scanning calorimetry (DSC) technique. In this investigation, DSC measurments were performed on a SETARAM SETSYS Evolution-1200 thermal analyzer on recycled aluminium alloy 2017A in the range of temperature from room ~25 to 700°C and different scan rates of heating at 5,10,15, 20 and 25°C min-1. The peak temperatures of the clusters, GP zones and hardening phases ’"and  Q from each heating rate were collected to calculate the activation energy associated with precipitation reactions in aluminium alloy 2017A using various mathematical models: the Kissinger, Ozawa and Boswell. The results (XRD, LM, TEM, DSC) show that both the θ and Q phases are strengthening phases, but the strengthening effect of the ",  phases is dominant. The strengthening phases, mainly ", ' increase the hardness during natural aging. The maximum hardness value 128HB was obtained after ~25h of natural ageing. The activation energy of precipitation of strengthening phase θ” in 2017A aluminum alloy determined by Kissinger, Ozawa and Boswell models are: 89.94  kJ· mol−1, 98.7  kJ· mol−1 and 94.33  kJ· mol−1 respectively and for θ’: 72.5  kJ· mol−1, 81.9  kJ· mol−1 and 77.2  kJ· mol−1 .