Numerical modelling of PLC effect induced flow figure formation during sheet metal forming of 5xxx aluminium alloys

During sheet metal forming processes, 5xxx-AlMg(Mn) alloys tend to form flow figures due to the so-called Portevin-Le Chatelier effect (PLC effect). To date, this visually apparent phenomenon has prevented such 5xxx sheet materials from being used for exterior automotive body components, despite their stable material states and excellent forming properties. Nevertheless, research has shown that the PLC effect and thus the formation of flow figures can be suppressed by comparatively high forming speeds. In this context, this paper presents an approach for numerical modelling of the PLC effect based on experimentally determined PLC curves, characterizing the relationship between strain rate and plastic strain at the onset of flow figure formation. The study focused on investigating the material behaviour of EN AW 5182 and EN AW 5754 alloys. The determined PLC curves were implemented in LS-DYNA with the 'DIEM' failure model by adapting strain rate-dependent forming limit curves (SRFLC) to realistically map the PLC effects. Subsequent numerical analyses enabled prediction of the strain-rate dependent flow figure formation on both test samples and a complex sheet metal component. Here, higher ram speeds prevented flow figures, which was confirmed by experimental forming tests. Thus, this paper provides a numerical method for designing sheet metal forming processes for the production of flow figure-free components made of 5xxx aluminium alloys, which could enable the use of such aluminium sheets for high-quality outer body components in the future.