Experimental and Numerical Studies on the Forming Behavior of High Strain Al-Mg-Si(-Cu) Sheet Alloys

Abstract

Al-Mg-Si(-Cu) heat-treatable alloys are characterized by a significant increase in hardness upon ageing compared to 6xxx series alloys with a copper content of Cu<0.15wt.%. With a higher amount of copper, the formability and ductility of the alloy are typically decreased compared to 6xxx alloys with a low content of Cu.The purpose of this paper is to discuss recent developments of high-strain 6xxx alloys for future automotive applications. The influence of copper content on the forming behavior of Al-Mg-Si(-Cu) sheet alloys was investigated. The examination was confined to four different alloys in total: Three of type AA6111 with varying Cu contents and a reference alloy type AA6016. All alloys were pre-aged at > 80°C after quenching and had a solute content of Si/Mg ratio in balance (wt.%).The forming behavior was characterized by tensile tests, bending tests, cup drawing tests and Nakajima tests. The experimental results are supplemented by numerical simulation. Hocket-Sherby's hardening law and Hill 90 yield criterion were used for the material modeling behavior. The Marciniak-Kuczynski model (M-K-model) approach was chosen to construct forming limit diagrams for all alloys.The study showed that forming behavior is strongly dependent on the type of alloy, the thickness, and natural aging, which is in turn influenced by the storage period and the quenching rate in sheet production. Up to a Cu content of 0.8wt.% the limiting drawing ratio is approximately equal to the reference alloy. With contents greater than 0.8wt%, an exponential drop of the formability is observed. Furthermore, the results of the cup drawing tests are compared to the numerical simulations in order to validate the simulation of parts with higher complexity. The results of this work contribute to the application of high strain 6xxx alloys in automotive applications