Temperature and strain rate influence on AA5086 Forming Limit Curves: Experimental results and discussion on the validity of the M-K model

Due to the high-strength to weigh ratio, corrosion resistance, good workability and weldability characteristics, aluminum alloys are increasingly used in many sectors. Researches on formability of aluminum alloy sheets have always been a hot topic these last few years while very few works taking into both temperature and strain rate effects on formability limits can be found in the literature. In this study, the formability of sheet metal AA5086 is investigated at different temperatures (20, 150 and 200 °C) and strain rates (0.02, 0.2 and 2 s−1) through a Marciniak test setup. Experimental results show that the formability of AA5086 increases with temperature and decreases with forming speed. Based on the analytical M-K theory, a Finite Element (FE) M-K model is proposed to predict the Forming Limit Curves (FLCs). A modified Ludwick hardening law with temperature and strain rate functions is proposed to describe the thermo-elasto-viscoplastic behavior of the material. The influence of the initial imperfection (f0) sensitivity in the FE M-K model is discussed and a strategy to calibrate f0 is proposed. The agreement between experimental and numerical FLCs indicates that the FE M-K model can be an effective model for predicting sheet metal formability under different operating conditions if the initial imperfection value is calibrated for each forming condition.