Leveraging transient mechanical effects during stress relaxation for ductility improvement in aluminium AA 8011 alloy

The mechanical behaviour during stress relaxation of metals has generated considerable interest in the recent years owing to its contribution to ductility. Most of the past studies were focused on ferrous alloys. In the present work, an attempt is made to systematically quantify the improvement in ductility during stress relaxation in AA 8011 aluminium alloy. Room temperature uni-axial tensile tests with single relaxation step were performed under different combinations of pre-strain, strain rate and relaxation time. The ductility was found to increase in all the cases. The parametric dependence of ductility improvement can be assessed using an empirical equation. It was found that the ductility improvement in aluminium is significant compared to SS 316 under similar conditions. The stress-time data obtained is modelled using a recently proposed logarithmic law and is found to fit the experimental data well. The underlying transient mechanisms responsible for ductility improvement are explored by conducting image based fractography analysis of the samples post failure. The fractography was complemented with nano-indentation technique to characterize the homogenization of internal stress.