Hemming Evolution of 6xxx Aluminum Alloys in the Course of Natural Aging Following the Continuous Annealing

The thermomechanical processing steps immediately following the continuous annealing in a production line were simulated in the lab to understand the evolution of hemming behavior of AA6016 and AA6005A in the course of natural aging (NA). After solution heat treatment and quench samples received various post-treatments namely pre-straining (PS) and pre-aging (PA) followed by NA. The results show that the hemming performance of both alloys significantly drop immediately after quenching followed by a milder decrease up to 1 month of NA. The significant drop of the work hardening and dynamic recovery rate during the first hour of NA after quench may explain the degradation of hemming. PS shows a similar effect as NA on the work hardening rate without affecting the dynamic recovery rate noticeably. PA decreases the work hardening and the dynamic recovery rate considerably.