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

Abstract

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 (1mm/s) and a drop weight test (1700mm/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 7µm. It is shown by the forming limit curves (FLC) that the formability increases with rising temperature. High punch velocity deformation at 1700mm/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.