Improvement of strength and ductility for a 6056 aluminum alloy achieved by a combination of equal-channel angular pressing and aging treatment

Incited by the aim of improving the strength and preserving a moderate ductility, the promising approach of a combined equal-channel angular pressing (ECAP) and aging treatment was applied to the 6056 Al-Mg-Si-(Cu) alloy. This method has been proven to be most effective for a small number of ECAP passes in the solid-solution condition and a following aging treatment, which is timed to enable precipitation hardening up to the peak strength on the one hand and microstructural recovery just before the onset of softening on the other hand. In this work, the evolution of hardness during post-ECAP aging and the effect of aging temperature and time on strength and ductility will be discussed. By means of low-voltage scanning transmission electron microscopy, the underlying microstructural features in terms of dislocation structure and precipitation characteristics will be presented. It has been found that peak aging especially at low-aging temperatures is suitable for achieving the desired high-strength combination, whereas-on the expense of some percent in the strengthening-the ductility is best in slightly underaged conditions. Compared to the initial peak-aged condition, an increase in strength of 27%, combined with a moderate ductility of 6.5% uniform elongation was achieved for peak aging at 150 A degrees C after two passes of ECAP.