Effect of Alloy Composition and Pre-Ageing on the Stretch Formability of 6xxx Automotive Sheet Alloys

In this study, the effect of Mg/Si ratio, Cu content and/or pre-ageing treatment (e.g. 100 degrees C for 2 h and/or 200 degrees C for 20 s) on the stretch formability of 6xxx alloys was investigated through their influence on the work hardening and strain-rate hardening behaviour using tensile testing and forming limit diagram tests. The results showed that a high Mg/Si ratio, a low Cu content and/or the employment of pre-ageing could deteriorate the stretch formability due to the decrease in work hardening and/or strain rate hardening capabilities. Moreover, the stretch formability was observed to have an opposite correlation with the paint-bake response of the alloys studied.