Influence of impurity level and processing parameters on local and macroscopic necking and failure parameters for 6000 series aluminium alloys

• An experimental workflow has been set up that allows determining local necking and fracture strain both in uniaxial and plane strain tensile conditions. • Applying this workflow on a variety of 6000 series Aluminium alloys where the amount of Fe and Mn was varied as well as the processing conditions provide a guide on the influence of these parameters on formability. • Correlations were obtained between local necking and fracture criteria and macroscopic tests including bending and limiting dome height. This work presents an experimental workflow which enables measuring local necking and fracture strains during uniaxial and plane strain tensile tests, using digital image correlation and optimized sample geometry. These parameters are compared with macroscopic parameters from these tensile tests, and to classical formability indicators, such as limit dome height or bending tests. This workflow is applied on a large experimental database of 6000 series Aluminium alloys with varying Fe and Mn content, representative of changing impurity levels. It is found that locally resolved parameters show a different sensitivity to the tested processing variations when compared to macroscopic indicators. Besides, the bending angle at failure is strongly correlated with the local fracture strain in plane strain tension and the limit dome height is correlated to the local necking strain. The results of this work demonstrate that using local strain measurements helps to better characterize sheet formability and emphasise the importance of considering the local behaviour at the fracture location to evaluate the effect of impurities on formability. The application of this workflow on our large experimental database evidences the effect of addition of Fe, Mn, and of cooling rate and changing the homogenization recipe, on the necking and fracture properties.