Quench sensitivity of Al–Mg–Si alloys: A model for linear cooling and strengthening

In this work quench-induced precipitation during continuous cooling of five Al-Mg-Si alloys is studied over a wide range of cooling rates of 0.05 K/min - 2x10^4 K/min using Differential Scanning Calorimetry (DSC), X-ray diffraction, optical microscopy (OM), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and hardness testing. The DSC data shows that the cooling reactions are dominated by a high temperature reaction (typically 500 °C down to 380 °C) and a lower temperature reaction (380 °C down to 250 °C), and the microstructural analysis shows they are Mg2Si phase formation and B’ phase precipitation on dispersoids, respectively. A new, physically-based model is designed to model the precipitation during the quenching as well as the strength after cooling and after subsequent age hardening. After fitting of parameters, the highly efficient model allows to predict accurately the measured quench sensitivity, the volume fractions of quench induced precipitates, enthalpy changes in the quenched sample and hardness value