Retrogression-Reaging Behavior in Aluminum AA6013-T6 Sheet

The kinetics of retrogression in a high-strength aluminum AA6013-T6 (Al-Mg-Cu-Si) sheet are investigated to determine retrogression heat treatments that allow subsequent reaging to approximately peak-aged hardness and strength. The goal is to combine retrogression with simultaneous warm forming of AA6013-T6 sheet. This new approach is termed retrogression forming. Differential scanning calorimetry is used to measure the activation energy of retrogression in AA6013-T6, which was determined to be 160 ± 30 kJ/mol. Heat treating experiments determine the change in hardness during retrogression as a function of time for temperatures ranging from 230 to 250 °C. The concept of temperature-compensated time is used to predict retrogression times and temperatures that allow for the recovery of nearly peak-aged strength through a subsequent reaging treatment. Different reaging heat treatments are investigated for recovering the hardness lost during retrogression.