The effect of heavy cold plastic deformation on the non-isothermal kinetics and the precipitation sequence of metastable phases in an Al-Mg-Si alloy

The kinetics and the precipitation sequence of metastable phases in an un-deformed and heavily deformed Al-Mg-Si alloy are investigated. The effect of plastic deformation, prior to annealing, is studied in terms of kinetic parameters variations during the precipitation reaction. Kissinger-Akahira-Sunose isoconversional method was applied to DSC data obtained for different constant heating rates. The results show a strong effect of plastic deformation on the activation energy value, particularly for early stages of precipitation where dislocations play a significant role. The increase in the activation energy value with plastic deformation has been related to a modification of the precipitation sequence: The beta' phase formation was promoted at the expense of the beta aEuro(3) one. The growth exponent, n, decreases gradually as increasing temperature, attaining constant values of 1.6 and 1.2 for later stages of precipitation, respectively, for the un-deformed and cold-rolled samples. These two values are consistent with beta aEuro(3) and beta' precipitates specifications. Furthermore, the activation energy was discussed in terms of separate activation energies for nucleation and growth.