Forming limit diagrams of twin-roll cast, rolled and heat-treated AZ31 as a function of temperature and loading rate

The influence of temperature and punch velocity on the forming limit behavior of twin-roll cast, rolled and heat-treated AZ31 was investigated. Therefore, the Nakajima test was performed using an electromechanical testing machine (1 mm/s) and a drop weight test (1700 mm/s) at different temperatures. For investigation of the local strains, the fractured specimens were studied by an optical strain measurement system. The initial Mg-3Al-1Zn-0.3Mn material has a strong basal texture and a recrystallized grain structure with an average grain size of 7 µm. It is shown by the forming limit curves (FLC) that the formability increases with rising temperature. High punch velocity deformation at 1700 mm/s leads to a decrease of formability. Microstructural examinations show that this is caused by high amounts of mechanical twinning and a constraint of dynamic recrystallization (DRX) which are temperature and punch velocity dependent mechanisms.